Beginners' botany

We have learned (in Chap. VI) that plants propagate by means of seeds. They also propagate by means of bud parts,—as rootstocks (rhizomes), roots, runners, layers, bulbs. The pupil should determine how any plant in which he is interested naturally propagates itself (or spreads its kind). Determine this for raspberry, blackberry, strawberry, June-grass or other grass, nut-grass, water-lily, May apple or mandrake, burdock, Irish potato, sweet potato, buckwheat, cotton, pea, corn, sugar-cane, wheat, rice.

Plants may be artificially propagated by similar means, as by layers, cuttings, and grafts. The last two we may discuss here.

Cuttings in General.—A bit of a plant stuck into the ground stands a chance of growing; and this bit is a cutting. Plants have preferences, however, as to the kind of bit which shall be used, but there is no way of telling what this preference is except by trying. In some instances this preference has not been discovered, and we say that the plant cannot be propagated by cuttings.

Most plants prefer that the cutting be made of the soft or growing parts (called “wood” by gardeners), of which the “slips” of geranium and coleus are examples. Others grow equally well from cuttings of the hard or mature parts or wood, as currant and grape; and in some instances this mature wood may be of roots, as in the blackberry. In some cases cuttings are made of tubers, as in the Irish potato (Fig. 60). Pupils should make cuttings now and then. If they can do nothing more, they can make cuttings of potato, as the farmer does; and they can plant them in a box in the window.

The Softwood Cutting.—The softwood cutting is made from tissue that is still growing, or at least from that which is not dormant. It comprises one or two joints, with a leaf attached (Figs. 158, 159). It must not be allowed to wilt. Therefore, it must be protected from direct sunlight and dry air until it is well established; and if it has many leaves, some of them should be removed, or at least cut in two, in order to reduce the evaporating surface. The soil should be uniformly moist. The pictures show the depth to which the cuttings are planted.

For most plants, the proper age or maturity of wood for the making of cuttings may be determined by giving the twig a quick bend: if it snaps and hangs by the bark, it is in proper condition; if it bends without breaking, it is too young and soft or too old; if it splinters, it is too old and woody. The tips of strong upright shoots usually make the best cuttings. Preferably, each cutting should have a joint or node near its base; and if the internodes are very short it may comprise two or three joints.

The stem of the cutting is inserted one third or more of its length in clean sand or gravel, and the earth is pressed firmly about it. A newspaper may be laid over the bed to exclude the light—if the sun strikes it—and to prevent too rapid evaporation. The soil should be moist clear through, not on top only.

Loose sandy or gravelly soil is used. Sand used by masons is good material in which to start most cuttings; or fine gravel—sifted of most of its earthy matter—may be used. Soils are avoided which contain much decaying organic matter, for these soils are breeding places of fungi, which attack the soft cutting and cause it to “damp off,” or to die at or near the surface of the ground. If the cuttings are to be grown in a window, put three or four inches of the earth in a shallow box or a pan. A soap box cut in two lengthwise, so that it makes a box four or five inches deep—as a gardener’s flat—is excellent (Fig. 160). Cuttings of common plants, as geranium, coleus, fuchsia, carnation, are kept at a living-room temperature. As long as the cuttings look bright and green, they are in good condition. It may be a month before roots form. When roots have formed, the plants begin to make new leaves at the tip. Then they may be transplanted into other boxes or into pots. The verbena in Fig. 161 is just ready for transplanting.

It is not always easy to find growing shoots from which to make the cuttings. The best practice, in that case, is to cut back an old plant, then keep it warm and well watered, and thereby force it to throw out new shoots. The old geranium plant from the window garden, or the one taken up from the lawn bed, may be treated this way (see Fig. 162). The best plants of geranium and coleus and most window plants are those which are not more than one year old. The geranium and fuchsia cuttings which are made in January, February, or March will give compact blooming plants for the next winter; and thereafter new ones should take their places (Fig. 163).

The Hardwood Cutting.—Best results with cuttings of mature wood are secured when the cuttings are made in the fall and then buried until spring in sand in the cellar. These cuttings are usually six to ten inches long. They are not idle while they rest. The lower end calluses or heals, and the roots form more readily when the cutting is planted in the spring. But if the proper season has passed, take cuttings at any time in winter, plant them in a deep box in the window, and watch. They will need no shading or special care. Grape, currant, gooseberry, willow, and poplar readily take root from the hardwood. Fig. 164 shows a currant cutting. It has only one bud above the ground.

The Graft.—When the cutting is inserted in a plant rather than in the soil, it is a graft; and the graft may grow. In this case the cutting grows fast to the other plant, and the two become one. When the cutting is inserted in a plant, it is no longer called a cutting but a scion; and the plant in which it is inserted is called the stock. Fruit trees are grafted in order that a certain variety or kind may be perpetuated, as a Baldwin or Ben Davis variety of apple, Seckel or Bartlett pear, Navel or St. Michael orange.

Plants have preferences as to the stocks on which they will grow; but we can find out what their choice is only by making the experiment. The pear grows well on the quince, but the quince does not thrive on the pear. The pear grows on some of the hawthorns, but it is an unwilling subject on the apple. Tomato plants will grow on potato plants and potato plants on tomato plants. When the potato is the root, both tomatoes and potatoes may be produced, although the crop will be very small; when the tomato is the root, neither potatoes nor tomatoes will be produced. Chestnut will grow on some kinds of oak. In general, one species or kind is grafted on the same species, as apple on apple, pear on pear, orange on orange.

The forming, growing tissue of the stem (on the plants we have been discussing) is the cambium (Chap. X), lying on the outside of the woody cylinder beneath the bark. In order that union may take place, the cambium of the scion and of the stock must come together. Therefore the scion is set in the side of the stock. There are many ways of shaping the scion and of preparing the stock to receive it. These ways are dictated largely by the relative sizes of scion and stock, although many of them are matters of personal preference. The underlying principles are two: securing close contact between the cambiums of scion and stock; covering the wounded surfaces to prevent evaporation and to protect the parts from disease.

On large stocks the commonest form of grafting is the cleft-graft. The stock is cut off and split; and in one or both sides a wedge-shaped scion is firmly inserted. Fig. 165 shows the scion; Fig. 166, the scions set in the stock; Fig. 167, the stock waxed. It will be seen that the lower bud—that lying in the wedge—is covered by the wax; but being nearest the food supply and least exposed to weather, it is the most likely to grow: it will push through the wax.

Cleft-grafting is practised in spring, as growth begins. The scions are cut previously, when perfectly dormant, and from the tree which it is desired to propagate. The scions are kept in sand or moss in the cellar. Limbs of various sizes may be cleft-grafted,—from a half inch up to four inches in diameter; but a diameter of one to one and a half inches is the most convenient size. All the leading or main branches of a tree top may be grafted. If the remaining parts of the top are gradually cut away and the scions grow well, the entire top will be changed over to the new variety.

Another form of grafting is known as budding. In this case a single bud is used, and it is slipped underneath the bark of the stock and securely tied (not waxed) with soft material, as bass bark, corn shuck, yarn, or raffia (the last a commercial palm fibre). Budding is performed when the bark of the stock will slip or peel (so that the bud can be inserted), and when the bud is mature enough to grow. Usually budding is performed in late summer or early fall, when the winter buds are well formed; or it may be practised in spring with buds cut in winter. In ordinary summer budding (which is the usual mode) the “bud” or scion forms a union with the stock, and then lies dormant till the following spring, as if it were still on its own twig. Budding is mostly restricted to young trees in the nursery. In the spring following the budding, the stock is cut off just above the bud, so that only the shoot from the bud grows to make the future tree. This prevailing form of budding (shield-budding) is shown in Fig. 168.