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 Mor- 
phology and Cytology, Iowa State College 
CONTENTS 
Page 
Part I.— Pollination Studies of Seed Pro- 
duction. 
Unsatisfactory Yields of Sweet-Clover 
Previous Investigations of the Polli- 
nation of Sweet Clover .... 
Outline of Pollinating Experiments . 
Structure of the Flowers of Melilotus 
alba .... 
Development of the Floral Organs of 
Sweet Clover 
Fertilization in Melilotus alba . . 
Development of the Seed .... 
Mature Pollen of Sweet Clover . . 
Germination of the Pollen .... 
Cross-Pollination and Self-Pollina- 
tion 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 
20 
21 
22 
Page 
Part L— Pollination Studies of Seed 
Production — Continued. 
Relation of the Position of the 
Flowers on Melilotus alba Plants 
to Seed Production 19 
Influence of the Weather at Blossom- 
ing Time upon Seed Production . 
Insect Pollinators of Sweet Clover . 
Effect of Moisture upon the Pro- 
duction of Melilotus alba Seed . 
Part EL — Structure and Chemical Na- 
ture 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 
WASHINGTON 
GOVERNMENT PRINTING OFFICE 
1920 
