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Sweet-Clover Seed

Chapter 3: SWEET-CLOVER SEED
By H. S. Coe
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About This Book

The work investigates causes of unsatisfactory seed yields in sweet clover through two linked studies. The first reports controlled pollination experiments that assess self- versus cross-pollination, insect exclusion and visitation, floral structure and pollen germination, and environmental factors such as moisture and weather on pod set and shedding. The second analyzes seed-coat anatomy and chemistry, comparing permeable and impermeable seeds, testing treatments that alter coat permeability, and relating coat structure to water absorption and germination. Methods, observations, and practical implications for improving seed production are presented.

UNITED STATES DEPARTMENT OF AGRICULTURE

BULLETIN No. 844

Contribution from the Bureau of Plant Industry
WM. A. TAYLOR, Chief
Washington, D. C. PROFESSIONAL PAPER August 11, 1920

SWEET-CLOVER SEED

Part I.—Pollination Studies of Seed Production

Part II.—Structure and Chemical Nature of the Seed Coat and its Relation to Impermeable Seeds of Sweet Clover

By H. S. Coe, formerly Assistant Agronomist, Office of Forage-Crop Investigations, and J. N. Martin, Professor of Morphology and Cytology, Iowa State College.

CONTENTS

Page
Part I.—Pollination Studies of Seed Production.
Unsatisfactory yields of sweet-clover seed 1
Previous investigations of the pollination of sweet clover 2
Outline of pollinating experiments 3
Structure of the flowers of Melilotus alba 4
Development of the floral organs of sweet clover 5
Fertilization in Melilotus alba 8
Development of the seed 8
Mature pollen of sweet clover 9
Germination of the pollen 9
Cross-pollination and self-pollination of sweet clover 10
Artificial manipulation of sweet-clover flowers 10
Seed production of Melilotus alba under  ordinary field conditions 13
Efficiency of certain kinds of insects as pollinators of sweet clover 14
Relation of the position of the flowers on Melilotus alba plants to seed production
 19
Influence of the weather at blossoming time upon seed production 20
Insect pollinators of sweet clover 21
Effect of moisture upon the production of Melilotus alba seed  22
Part II.—Structure and Chemical Nature of the Seed Coat and its Relation to Impermeable Seeds of Sweet Clover.
Historical summary 26
Material and methods 30
Structure of the seed coat 31
Microchemistry of the seed coat 33
The seed coat in relation to the absorption of water 34
A comparison of permeable and impermeable seed coats 34
The action of sulphuric acid on the coats of impermeable seeds  35
Literature Cited 36