SOME PHASES OF STRUCTURE AND DEVELOPMENT OF 



GARDEN PEA AND WHITE SWEET CLOVER SEEDS 



AS RELATED TO HARDNESS 



By L. Edwin Yocum 



Plates 5 and 6 



Hard seed coats are very common among the Leguminosae. Guppy 

 (7) mentions 32 legume seeds in a list of 43 plants Avhose seeds are 

 more or less hard. Harrington (8) has found in hand hulled seeds 

 the folloAving percentages of hard seeds : alsike clover, 92% ; red 

 clover, 92 9r ; white clover, 98% ; and white sweet clover, 98%. There- 

 fore, it is of vast economic importance to determine some way of 

 inducing all the legume seeds to germinate soon after sowing rather 

 than months or years later, which is often the cause of a poor stand 

 of clover. The purpose of this paper is: (1) to trace the develop- 

 ment of the garden pea and white sweet clover seed coats, and (2) 

 to find out the chemical composition of the cell walls. It is hoped 

 that these factors may throw light on the cause of hardness and sug- 

 gest some method of overcoming the hardness of the seed coats which 

 will be more practical to the farmer than any of the present methods. 

 The ]\lalpighian cells have been found to be most important as 

 regards hardness, and therefore most emphasis will ])e put on the 

 study of that layer of cells. 



Hard seeds are considered as those failing to absorb water when 

 under favorable conditions for three or more days. 



Historical 



Seed coats have been investigated from time to time since 1667 

 when Malpighi described the cells now bearing his name. Russow, 

 1871, studied the light line with polarized light and came to the con- 

 clusion that it had less water tluni other ])arts of the cell. Pammel, 



(12) 1885, examined several of llic L( (/utninosae. and again. Pammel, 



(13) 1899, published a monumental work on the anatomical char- 

 acters of the Leguminosac, with excellent figures, and an extensive 

 bibliography. 



( vr, ] 



