Grasses

CHAPTER VIII.

THE FRUIT AND SEED.

The stigma of an ordinary grass consists of two divaricating plume-like structures composed of thin-walled cells. When the paleæ open these stigmatic plumes protrude, one on either side, and readily catch pollen shed from the dangling stamens and carried by the wind, and since the pollen of the same flower is usually shed at a time when the stigmas of many neighbouring plants are mature, there is every opportunity for cross-fertilisation. (Fig. 33.)

In some cases, however, e.g. Anthoxanthum, Alopecurus, the flowers are proterogynous, the stigmatic plumes being ready for pollination some time before the pollen is shed from the anthers of the same flower; whereas in most of our grasses the pollen begins to scatter before the stigmas Fig. 37. Pollen-grains adherent to the papillæ of the stigma, on which they germinate, sending the pollen-tubes down between the cells. Kerner. × about 100. are ready (protandrous). Among exotic grasses, many are diœcious or monœcious—i.e. the flowers contain stamens only or ovary only, on each plant, or on different inflorescences of the same plant respectively—and even in our own Holcus and Arrhenatherum this state of affairs is partially represented, since one flower of the spikelet is male only.

In some grasses, e.g. Rye, however, it appears improbable that cross-fertilisation ever occurs, since the paleæ do not open, and the pollen falls on to the stigma direct; and in Leersia and the foreign Amphicarpum the spikelets are completely cleistogamous, those of the latter being on stalks close to the ground which push the flowers into the soil, where pollination and fructification are accomplished.

Hybrid grasses are by no means uncommon. To say nothing of the numerous cross-bred Wheats and Barleys, artificial hybrids have been raised between Wheat and Rye. In the Maize an astonishing number of selected cross-breeds have been obtained, and, among Fig. 38. Longitudinal median section of the caryopsis of a grass—e.g. Lolium (× about 35). p, pericarp; t, attachment to axis; m, position of micropyle; E, endosperm; A, its aleurone layer; l, folded leaves of plumule; r, radicle; r´´, secondary roots; RC, root-cap; s, scutellum. The dark line e represents the surface where the face of the scutellum is applied to the endosperm and where absorption of the latter takes place.others, certain forms in which the seeds have a violet outer layer and a sugary endosperm, are found to transmit these characters to the resulting seed of a variety which would normally have produced seed with white outer layers and starchy endosperm, if the pollen of the former is used on the stigma of the latter. Such direct influences of the pollen are termed Xenia.

When the pollen-grain, having adhered to the hairy stigma, has begun to germinate, the resulting pollen-tube creeps down between the cells of the stigma, and hands over its enclosed nuclei to the embryo-sac, where fertilisation of the egg-cell is accomplished, by the fusion of one of the pollen nuclei with the nucleus of the egg-cell. As the resulting embryo developes, the sac becomes filled with endosperm-cells charged with starch-grains or sugar, and in the ripe seed the embryo is always found affixed laterally and below to this endosperm—a point of distinction from Sedges, where the embryo is buried in the endosperm.

The ripe seed fills the ovary, and its outer walls usually fuse with those of the carpel, forming the well-known Caryopsis or “grain."

If such a “grain" is carefully examined, three chief parts are visible in addition to the embryo. (Fig. 38.) Firstly, we find on the outside the fused seed-and fruitcoats, differing in the number of layers and in the microscopic characters of the cells, some of which characters can be employed in diagnoses. (Fig. 39.)

Secondly, the great mass of the “grain" internally is composed of delicate cells filled in most cases with starch-grains, the sizes, shapes and arrangement of which can also be employed for diagnoses—e.g. the compound grains of the Aveneæ and Festuceæ are different from the simple polyhedral or rounded grains of the Andropogoneæ and Maydeæ, and some races of Maize have sugar and soluble starch instead of grains of the latter.

Fig. 39. Transverse section (highly magnified) through a grain of Brachypodium pinnatum taken about half-way up. 1, epidermis; 2, pericarp; 3, remains of the true seed-coat; 4, vascular bundle; 5, remains of nucellus; P, epidermis of nucellus; G, aleurone layer: remarkable in being several cells thick; E, endosperm. Harz.

Thirdly, the outermost layer or layers of cells of the endosperm are filled with proteids, and are known as the Aleurone layer. (Fig. 38, A.)

The embryo consists of the folded embryonic leaves in bud (plumule) above, which will grow up on germination as the shoot or “spear," the short primary root (radicle) below, with in many cases two or more secondary rootlets Fig. 40. Triodia decumbens. a, “seed," nat. size; b, ditto, × 6. Note the basal hair-tuft and rachilla, and the ciliate, toothed outer palea with a short awn-point, enclosing the inner more delicate palea. Between the two lies the caryopsis. Nobbe.already showing in its tissues, and from the common “collar" uniting these a more or less prominent shield-shaped organ (scutellum) standing out laterally in contact with the endosperm, the dissolved contents of which it absorbs on germination. (Fig. 38, s.)

Although typical grasses form a caryopsis as described, exceptions occur. In the exotic Sporobolus, Eleusine, Crypsis and Heleochloa the fruit becomes truly dehiscent, the seed being loose in the fruit, and the latter opens and allows it to fall out; and in many Bamboos the seed is loose in the achene, while in a few cases—e.g. Melocanna—the fruit is fleshy and may be as big as a walnut.

Returning to the typical grasses. When the fruit ripens in the spikelet, several events may happen.

In most of our grasses the caryopsis comes away trapped between its two paleæ, and the latter bring away with them the small piece of the axis of the spikelet on which they stand: this bit of axis—the rachilla—often affords valuable characters in diagnosis. (Fig. 41.) It is the pair of paleæ enclosing their caryopsis which goes by the name of “seed" in most of our grasses. (Fig. 40.)

In a few cases, however, e.g. Panicum, the spikelet comes away as a whole, so that here the “seed" consists of the glumes, enclosing one, two or more pairs of paleæ with their contained caryopses.

Fig. 41. Diagram of a spikelet of a grass—e.g. Festuca—comprising six matured flowers and their paleæ, embraced by the two glumes (g¹g²) at the moment of disarticulation as the fruits ripen. The small piece of axis (a) left attached to each segment is the rachilla R. At p² the tip of the inner palea is visible protruding from the outer one p¹: in the rest it is still enclosed in the latter.Even among our native grasses, however, cases occur where the separation takes place below some of the glumes, and so the “seed," as met with in samples, consists of glumes as well as enclosed paleæ and caryopsis—e.g. Anthoxanthum, Alopecurus, &c.—and some care is necessary in examining grass “seed" in these circumstances (see p. 134).

Interesting biological adaptations are met with in the distribution of grass “seeds." The very small and light fruits of Agrostis easily fall and are scattered by the wind, but in many cases the glumes (Holcus) or paleæ (Briza) are expanded and serve as “wings" offering extensive surfaces to the wind. In Arundo, Calamagrostis, Aira, &c., fine silky hairs attached to the rachilla serve a similar function, reminding us of the coma of true seeds and the pappus of Composites. In Hordeum jubatum of the prairies, the axis breaks up and the disarticulated portions with their attached tufts of fruits are blown away by the wind, and something similar occurs in our own H. murinum to a less extent. In the exotic Spinifex whole heads of fruits are thus detached and blown over the sands as “tumble weeds.”

In Stipa pennata we have an example of perhaps the most complex of all such adaptations: the exceedingly long awn terminating the palea is plumose at the upper end and twisted below, and the hard sharp rachilla at the base of the fruit is furnished with short, stiff hairs directed upwards. The plumed awn serves as a wind surface, the whole fruit flying like an arrow through the air. The stiff hairs below serve to fix the lower end between particles of soil, and by their alternate drying and wetting, the warping of these and of the twisting and untwisting awn drives the sharp base into the soil. (Fig. 42.) Similar mechanisms exist in Avena and others.

These bristles and awns also subserve dissemination in other ways, especially by clinging to the wool and fur of sheep and other animals, and cases occur where the twisting awns and reflexed hairs on the hard pointed fruit-base drive the latter into the bodies of sheep with fatal effects—e.g. Stipa capillata in Russia, S. spartea in America, Aristida hygrometrica in New Zealand, Heteropogon contortus in New Caledonia.

Fig. 42. Awned fruit of Stipa. The reflexed stiff hairs and hard point favour penetration into the soil. The long twisted awn performs hygroscopic movements, and its terminal plume offers surface to the wind. Lubbock.

America, Aristida hygrometrica in New Zealand, Heteropogon contortus in New Caledonia.

Fig. 43. Poa annua. d, the “seed," nat. size; a and b, ditto, × about 7; c, caryopsis, natural size (above) and × about 7. Note the ribs and silky keel. No "web." Nobbe. Cf. Figs. 54-56. The driving action of even small reflexed asperities on awns is well illustrated by the fruits of Hordeum, which are often made by children to creep up the sleeve.

When we come to examine the external features of the “seeds" of grasses—usually the caryopsis enclosed in one or more paleæ, but sometimes in glumes as well—the following diagnostic characters are of importance.

The size varies from lengths of 2 mm. or less (Poa, Aira) (Figs. 43, 44) to 15-20 mm. or more (Arrhenatherum) (Fig. 47) and distinction must be made between the various characters of the caryopsis devoid of its coverings (paleæ, glumes) and such as really belong to the latter.

The caryopsis proper may be short and stout and devoid of a groove—"Millet-seed" type (Fig. 45)—but is oftener elongated, like a grain of Wheat, and then has the characteristic longitudinal groove on the face opposite that where the embryo is situated (Fig. 46). Details of shape—e.g. cylindroid, fusiform, flattened, &c.—are also of diagnostic value.

In many cases the “seed," consisting of the caryopsis closely compressed between the paleæ, is boat-shaped, e.g. Lolium perenne, Festuca elatior. If this “boat" is long and narrow it may be termed barge-shaped, e.g. Brachypodium sylvaticum, &c. (Figs. 71, 72): if short, broad, and open or shallow, the term coracle-shaped seems to apply, e.g. Bromus arvensis (Fig. 73).

Fig. 46. Boat-shaped “seed" of Glyceria fluitans. a, nat. size; b and c, × about 6. d, caryopsis, × about 10. Note the 5-7 strong nerves, and the slender cylindrical rachilla. Cf. Figs. 57 and 58. Nobbe.

Further important distinctive characters are obtained from the absence or presence of awns, and the peculiarities—length, Fig. 49. Agrostis Spicaventi. c, “seed," nat. size; a and b, ditto, × about 9. The long slender awn is inserted below the bifid tip of the palea. Nobbe. stiffness, &c.—of the latter. The awns may be straight, hooked, or kneed (i.e. sharply bent); twisted or not; smooth or serrulate. They may be inserted at the base or near the middle of the back of the investing palea, or glume, or near its apex, as indicated by the terms basal, dorsal, sub-terminal (see Figs. 47-50).

Some difficulty arises in connection with terminal awns. In some cases there is a true awn—i.e. a distinct bristle or hair—at the apex of the palea, and apparently continuing its substance without interruption; but in most instances close examination shows that this awn arises from between two minute teeth, and is really inserted at the back of the slight depression between them—e.g. Lolium temulentum (Fig. 48), Brachypodium pinnatum (Fig. 77), &c.

In another class of cases the awn appears to be really the prolongation of the palea—e.g. Nardus (Fig. 81), Festuca Myurus (Fig. 80), &c.—and when it runs out into a distinct bristle we may speak of a terminal awn without staying to discuss whether or no it is really terminal in development.

In Arundo, Cynosurus and some Fescues, where the palea tapers off into a stiff long point, I have not spoken of it as an awn, but have described the palea as tapering into a sharp point (awn-point). It must be admitted that the distinction is somewhat artificial, but it has its advantages in practice.

The rachilla (Fig. 41), when present, often affords good characters, and in a few cases is relied on for the distinction of “seeds" otherwise much alike—e.g. Lolium perenne and Festuca elatior; and similarly with the presence or absence of hairs (Digraphis, Arundo, &c.) or “web" (Poa) at the base of the “seed." (Figs. 55, 69.)

On germination the primary root of the embryo usually emerges and at once plunges into the soil, but soon ceases to grow, and the secondary roots (and subsequently adventitious rootlets from the lower internodes) soon give the peculiar fibrous character so well known in grass-roots.

The plumule either pushes out from the same end of the caryopsis as the root (e.g. Wheat, Rye) or drives its way between the coats to the opposite end (e.g. Barley) and appears as a pointed cylinder of rolled leaves (the "spear") the outermost of which is sheath only, no lamina being developed. As Darwin showed, the pointed apex of such a plumule is hardened, facilitating the piercing of the soil above, and when the blade attains the open air it performs spiral movements during growth, indicating that similar attempts to rock from side to side have aided the plumule in forcing its way through the soil. It has also been shown that the apices of roots and plumules are sensitive to differences of temperature, of light-intensity, moisture and contact, all of which aid the seedling in establishing its position in the soil and in liberating the "spear." For particulars the student should read Darwin’s Power of Movement in Plants.

With regard to the established seedlings of grasses, many interesting details of structure are to be found in them. I have not sufficient material to draw up a diagnostic arrangement of grass-seedlings, but it is evident that such could be done. It may be useful to illustrate this by the following tabular view of the characters of the larger seedlings of our common cereals, in part adapted from Vesque and Percival; though I find that some variations may occur, especially in the development of the auricles.

Seedlings.

I. First expanded aerial leaves broad, bright green, with 18-24 ribs.

Barley.

The blade tends to twist to the left: auricles, when well developed, long, pointed, and claw-like, embracing the glabrous sheath in front. Ligule long, membranous, pointed and irregularly toothed. The plumule emerges at the upper end of the grain, and the embryo has 5-6 secondary roots.

II. First aerial leaves narrower, with not more than 11-13 ribs.

A. Ligule long, rounded and toothed.

Wheat.

The blade tends to twist to the left: auricles filiform and embrace the densely pubescent sheath. Leaves green. Embryo with three roots.

B. Ligule short and toothed. Leaves with a reddish cast.

(a) Blade and sheath softly hairy, the latter with scattered long hairs, the former tending to twist to the left.

Rye.

The first leaf-sheath purple. Auricle-claws more triangular and smaller than those of wheat, and the accompanying bristles are fewer and shorter. Embryonic roots four.

(b) Blade and sheath glabrous or merely ciliate or silky, the former tending to twist to the right.

Oat.

Auricles filiform. The plumule emerges above. The embryo has three roots.

A curious phenomenon is observed in some grasses growing in high latitudes, or mountainous regions, or in moist situations. The flowers, or even entire spikelets, grow out into minute leafy buds, with rudimentary roots at the base, and fall off like the bulbils of other monocotyledons, taking root directly in the damp soil. The phenomenon must be looked upon as a case of apogamy, since the development of sexual organs is entirely passed over; the parts which would normally have become ovary and stamens being transformed into leaves. In some species or varieties—e.g. Poa alpina, Festuca ovina—this viviparous condition may coexist with normal flowers and spikelets; in others—e.g. Poa laxa, var. stricta—only the viviparous state occurs.

In the following arrangement the student should note that the terms “Seed" and “Fruit" are used in the ordinary sense of the farmer and seedsman: by the former is meant the “seed" as it comes in samples into the market, when the true fruit or grain (Caryopsis) is almost invariably invested by adherent “chaff"—i.e. paleæ or glumes or both. When the word Caryopsis is employed, I mean it strictly in the botanical sense explained above. In Hordeum, for example, we never see the true fruit, the grain consisting of the caryopsis with paleæ so closely adherent to it, that we are apt to take them as part of the grain itself. The true seed, in the strict botanical sense, is never seen as a naturally separate organ in our native grasses; and, as already explained, only very few exotic grasses ever shed it—e.g. Sporobolus.

CHAPTER IX.

CLASSIFICATION OF GRASSES BY THE "SEEDS" (GRAINS).

I. “Seed" rounded (Millet-seed12 type). Caryopsis ovoid or sub-globose, devoid of distinct groove, and distending the awnless paleæ, or falling out free.

A. Glumes cuspidate, “fruit" yellowish.

Phleum pratense.

The student should familiarise himself with the “seed" of Phleum pratense, as a type, and an important grass easily obtained pure, but sometimes with minute round seeds of weeds intermixed.

Phleum pratense, L. (Fig. 45).

Palea 2·3 mm. long, five-ribbed, with a short point, delicate but hard, smooth, with a silvery lustre. Inner pale two-nerved. Closely investing the yellow-brown

caryopsis, which easily falls out and is ovoid-acute, about 2 mm. long by 1 broad, and finely punctate.

The much rarer P. arenarium and the very rare P. Bœhmeri and P. asperum also come here.

Phleum is not easily confounded with any other of our grasses, and Briza and Glyceria are almost the only other common grasses of about the same size of which the caryopsis often falls free from the palea ("naked fruits"). Glyceria is longer and corn-shaped, and Briza usually larger. Anthoxanthum and Phalaris are easily distinguished. Agrostis is smaller and “corn-shaped." Certain species of Panicum present resemblances, but the enveloping paleæ, &c. are very different. Melica also occurs as “naked fruits,” but is rarely seen, and its colour and brilliant lustre distinguish it.

B. Glumes not cuspidate. “Fruit" not yellow.

(a) “Fruit" white, owing to the closely investing palea.

Milium effusum.

A common grass, but not often met with in “seed" grasses. It is eagerly eaten by birds.

Milium effusum, L. (Fig. 52).

Palea about 3 mm. long, with Fig. 52. Milium effusum. "Seed," a, nat. size; b and c, × 7. Nobbe. few nerves, closely investing the caryopsis: the seed is ellipsoid-acute, slightly compressed, and 2·2-2·7 mm. long. The inner pale becomes hard and shines like porcelain.

(b) “Fruit" dark-brown shining; slightly flattened and grooved.

Melica.

Melica is rarely met with as “seed." When it is, it has to be distinguished from the other “Millet-seed" types which readily fall as naked fruits—see Phleum, Milium, &c. Agrostis, Glyceria and other corn-shaped “seeds" are easily distinguished.

Melica nutans, L. (Fig. 53).

"Seed" coracle-shaped. Palea broad, parchment-like, elliptic convex, 5-6 mm. long, 5-7 nerved and keeled, awnless, loose, purplish. Caryopsis ellipsoid-acute, 2-3 mm. long, and easily separating, wrinkled, dark shining brown as if lacquered.

Fig. 53. Coracle-shaped “seed" of Melica nutans, showing the broad, ribbed and keeled palea (c), and small rachilla (d). a, the “seed," nat. size; c and d, ditto, × 8; b, the caryopsis, nat. size; e and f, ditto, × 10. Nobbe.

M. uniflora, Retz. is commoner and very similar, but neither is often met with in “seed" grass, except as impurities among Fescues.

The rare Panicum Crus-galli and allies, and the rice-like Leersia oryzoides as well as Cynodon Dactylon, come here.

Panicums may occur in grass “seed" from America: Burchard describes them in detail.

II. “Seed" long (Corn and Barley type). Caryopsis oblong or flattened, usually trapped between the boat-shaped paleæ: if otherwise, with an awn.

A. “Seed" awnless. There may be a short sharp point to the palea (mucronate), but no prominent hair-or bristle-awn exceeding half the length of the palea.

(a) A “web" or tuft of hairs at the base or on the rachilla.

(1) Hairs of basal tuft silky and erect.

✲ Pencil of hairs as long as palea or longer.

Calamagrostis lanceolata, Roth.

Palea 3 mm. long, thin, two-toothed and with a short bristle at the apex.

Other species of Calamagrostis are awned. None occurs as an ordinary impurity in “seed."

Arundo Phragmites, L.

Palea narrow and long, 10-11 mm., delicate, entire, tapering to an acuminate point, violet, three-nerved, smooth. Caryopsis about 2 mm. A pencil of long silky hairs on the rachilla.

The long acuminate point is almost an awn.

Calamagrostis also has long basal hairs: both are useless grasses agriculturally. For Glyceria see note, p. 146. Avena, Aira and Psamma are easily distinguished.

✲✲ Pencil of hairs short.

† Palea mucronate, 11-12 mm. long: caryopsis 4·5 mm.

Psamma arenaria.

Digraphis differs in the stout caryopsis, smaller size, double hair-tuft. Arundo has a long pointed palea and long silky basal hairs and is larger.

Psamma arenaria, Beauv.

Palea 11·5 mm. ovate-lanceolate, papery, 4-5 nerved, as rolled round the fruit about 1·3 mm. diameter, yellow, and with a small tuft of stiff fine hairs at the base. Mere trace of awn, sub-terminal. Fruit 4-5 mm. long, obovate, pale-brown.

A shore-grass, not often seen as “seed": more valuable as a sand-binder than as fodder, though the young shoots are grazed.

†† Palea acuminate, and only about 4 mm. long: caryopsis 1·4 mm.

Digraphis arundinacea.

A Fen-grass, but coarse and not in use except the young growth, and for thatching.

Digraphis arundinacea, Trin.

Paleæ ovate-lanceolate, nerveless and awnless, but silky with double basal hair-tuft, and polished at the base; smooth, hard and shining, and closely investing the caryopsis which has no groove. Dark grey in colour. The glumes are without awns or wings, and are left behind.

The allied Phalaris canariensis has wing-like keels to the glumes.

Triodia also comes into this group, with short basal hairs; but its broad ciliate palea, 6 mm. long, has a short mucronate point between two teeth (Fig. 40).

(2) Hairs at the base forming a fluffy “web." Paleæ thin, 2-3 mm. long.

Poa pratensis. P. trivialis. P. compressa. P. nemoralis.

The “seeds" of Poa proper are nearly all small—not more than 3-4 mm., more or less lanceolate, with tough, keeled glumes, and when “webbed" tend to adhere together as if stuck with cobweb. The keeled glumes give them an angular appearance—triangular in section—and make them tend to lie on the side. Rachilla evident. Nerves of paleæ distinct.

Poa pratensis, L. (Fig. 55).

"Seed “ 2-3 mm. long, brownish: caryopsis about 1-1·5 mm. Outer palea acute, indistinctly 3-5 nerved, edges and keel, silky; margins overlapping the hyaline inner palea.

The “web" looks like hyphæ of a mould.

Caryopsis ellipsoid-acute, with traces of the stigma. It falls easily. No distinct groove, section somewhat triangular. Rachilla truncate.

Poa compressa, L.

Palea obtuse, nearly glabrous and nerveless, or faintly 3-5 nerved and with a faint web. It is close to P. pratensis.

Poa trivialis, L. (Fig. 56).

"Seed" 2-2·5 mm., and with a bluish or bronzed cast. Caryopsis 1-1·5 mm.

Palea acute, distinctly five-ribbed, glabrous, the margin scarcely overlapping. Caryopsis grooved, blunt and more tightly held in the palea.

P. trivialis differs from P. pratensis chiefly in the distinct ribs and smoother palea, grooved caryopsis, and bluer hue.

P. nemoralis, L., hardly differs from P. trivialis, but the paleæ are sub-acute, nerves obsolete, and scarcely hyaline at the margins. The “seed" is shorter and more acute, and the colour less pronounced, and with hardly a trace of hairs (Fig. 54).

When the basal hairs are absent this should go with P. annua, &c. (see p. 146).

It is practically impossible to distinguish these species by the "seed." Care is necessary to distinguish Kœleria, which is somewhat larger in size, keeled, compressed and nerved similarly, but is more pointed and curved and paler yellowish white in colour. Hard and devoid of web or hairs. Aira is distinguished by the awn: Agrostis by the very different paleæ and caryopsis.

The other Poas are devoid of web, though they may have hairs below, and require very careful examination. The whole group is excessively difficult to deal with in “seed," and a special study of it is needed, since several species are important, and it forms a type.

(b) No web or pencil of hairs below the “seed."

(1) Apex of palea rounded, blunt, notched, or at most bluntly pointed, but with no trace of awn-or bristle-tip.

✲ Palea inflated, round-backed and somewhat winged, membranous.

Briza media. B. minor.

Briza media, L.

Paleæ blunt, 2·5-3 mm., without lateral projections, markedly convex—almost conduplicate; nerves several. Caryopsis ovoid, 1·5-2·5 mm., dark brown.

Sometimes called a good grass, but meagre and only found in poor meadows in this country.

It should perhaps go with the “Millet-seed" type and should be compared with Phleum, Melica, Panicum, &c. “Seed" seldom met with.

B. minor is smaller.

✲✲ Paleæ not inflated or winged.

† Paleæ broad, flat and truncate, prominently three-ribbed. Caryopsis 2 mm. long.

Catabrosa aquatica, Beauv.

Cattle like it, but it only grows in ditches &c. in water-meadows: distinction from Glyceria aquatica easy if the paleæ are examined.

†† Paleæ acute or sub-acute, boat-shaped.

⊙ Paleæ and “seed" at least 6-8 mm. long.

≡ Rachilla flattened or angular, and tapering below.

Lolium perenne.

Occasionally awned, and then less easily distinguished from L. temulentum. One of our most valuable grasses. It forms a distinct type of boat-shaped “seeds."

Lolium perenne, L. (Fig. 57).

Palea distinctly five-ribbed, glabrous, oblong-lanceolate, obtuse or sub-acute, awnless, about 7 mm. long. Margins membranous. Inner palea nearly as long, delicate, ciliate.

Rachilla short, flattened and angular, tapering below (see Festuca elatior).

Caryopsis about 3·5 mm. long, obovate, yellowish brown.

Although Bromus mollis, Holcus lanatus, &c. occur as impurities, they are easily distinguished: the real difficulties are with Festuca elatior and F. pratensis.

≡ ≡ Rachilla cylindrical.

Festuca elatior.

This is an important grass, and should be thoroughly mastered as a type of the boat-shaped “seed."

This, with Lolium, Agropyrum, other Fescues, and even some Bromes and Poas, will give trouble until the student thoroughly masters the importance of the minute characters of size, nervature, of the rachilla, awn, palea, &c.

Festuca elatior, L. (var. pratensis) (Fig. 58).

Palea ovate-lanceolate, five-nerved, slightly scabrid, with a slight membranous margin and cilia, rounded back, and no awn. 6-7·5 mm. long.

Caryopsis oblong-obovate, somewhat flattened, hardly grooved and adhering to the paleæ, about 3-3·5 mm. long.

Rachilla cylindrical, smooth.

The other varieties of F. elatior cannot be distinguished by the "seed" alone: in my samples F. elatior proper is longer than F. pratensis, and both have occasionally a trace of awn. Var. arundinacea has a more acuminate, stiff point. Festuca pratensis has its palea as a rule somewhat more acute than Lolium perenne, and the flatter tapering rachilla of the latter is more closely appressed to the palea. The caryopsis of Festuca also tends to adhere to the paleæ.

⊙⊙ Paleæ and “seed" at most 3-3·5 mm. long.

≡ Palea devoid of hairs or keel, notched or blunt, and with no trace of awn.

Δ Palea hyaline, nerves indistinct. Tips notched or blunt.

Agrostis alba.

There is occasionally a very short basal hair (awn).

Agrostis and Aira will present difficulties to the beginner, not only on account of their small sizes, but also from the variability as regards awns, basal hair-tuft, &c. None are of value, and most of them are weeds.

Agrostis alba, L. (var. stolonifera).

Palea enclosing the fruit 1·8-2 mm. long, white, delicate, membranous, with a blunt notched apex and three (or five) nerves: occasionally there is a fine kneed basal awn, not projecting.

The glumes may remain attached: the outer has a serrulate keel, and often a violet hue. No awn. About 2-3 mm.

Caryopsis about 1·1 mm. long, oblong, yellow, corn-shaped, furrowed, shining through.

A. vulgaris, L., is a variety with slightly smaller fruits, no awn, and usually three nerves to the palea, but they cannot be distinguished with certainty by the "seed." Rachilla obsolete.

The colour of the glumes may vary considerably and is sometimes yellow.

The absence of awn, rachilla, and basal hairs distinguishes Agrostis from Aira.

ΔΔ Palea membranous, ribbed, tips scarious.

Glyceria aquatica.
G. fluitans.

Glyceria aquatica, Sm.

Palea strongly 5-7 ribbed, obtuse and scarious, about 4 mm. long. Green with a purple cast. Caryopsis dark-brown, about 2 mm. long.

Inner palea punctate. Rachilla slender and cylindrical.

Glyceria fluitans, Br., is very similar, but longer (6 mm.) and more slender; the palea scabrid with truncate or ragged tips, and the inner palea not punctate. Yellow. (Fig. 46.)

Glyceria aquatica and G. fluitans are sweet grasses of value in water-meadows only. The “seed" is not often met with.

Not only with the Poas, but also with Catabrosa are there difficulties in determination. Molinia and Kœleria also present difficulties with Glyceria: the former has fewer and feebler nerves. Digraphis and Arundo are easily distinguished by the basal hairs.

≡ ≡ Palea acute and somewhat compressed and keeled, and with hairs on the ribs. Tips nerved.

Poa annua. P. maritima. P. distans. P. rigida. P. loliacea. P. bulbosa. P. alpina.

Their “seeds" are all small, about 2-3·5 mm. only, and angular, brown, and present many difficulties (see note, p. 141).

Poa annua, L. (Fig. 43).

Palea 3·5 and caryopsis 2 mm. long, so that the “seed" is much larger than P. trivialis, and there is no web. Minutely silky-hairy on the keel, and the ribs are strong for a Poa.

Poa alpina, L., has the palea five-ribbed with stiffish hairs below, but no web. Bronzy green-violet. “Seed" 3-3·5 mm. long. Caryopsis 1·5-2 mm., and slightly grooved. It is rare in England, and is interesting as it becomes viviparous in Alpine situations.

(2) Apex of palea distinctly pointed, acuminate or mucronate, but not giving rise to a true, long, bristle-like awn.

✲ Palea acuminate—i.e. taper pointed.

† Not compressed or obviously keeled.

Festuca ovina. F. sylvatica. Cynosurus cristatus.

It is doubtful whether these should not be regarded as awned: if so they come near Nardus—see p. 130.

Festuca ovina, L. (Fig. 59).

Palea rounded on the back, narrow, terete-lanceolate and five-nerved, tip scaberulous and drawn out to a stiff scabrid point half as long as the palea, or less. About 3-4 mm. long without the tip-point, 4-5·5 mm. with it. Rachilla obliquely truncate and concave at its apex.