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 



Part I. — Pollination Studies of Seed Pro- 

 duction. 



Unsatisfactory Yields of Sweet-Clover 



Seed 1 



Previous Investigations of the Polli- 

 nation of Sweet Clover .... 2 

 Outline of Pollinating Experiments . 3 

 Structure of the Flowers of Melilotus 



aiba 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-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 



of Seed 



Page 



Part h — Pollination Studies 

 Production — Continued. 



E elation 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 . 20 

 Insect Pollinators of Sweet Clover . 31 

 Effect of Moisture upon the Pro- 

 duction of Melilotus alba Seed . 22 

 Part n. — 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 



