1923] Garden Pea and White Sweet Clover 79 



develops more than two or three rows of large cells. The garden 

 pea forms six to eight rows of cells in the inner integument but 

 never forms the cells so compactly as in the outer integument ; how- 

 ever, the two gradually shade off together. The inner integument in 

 both cases soon partially breaks down. 



The outer integument in sweet clover is made up of from five 

 to eight rows of cells. The garden pea has from six to ten layers 

 of cells in the outer integument. The former number is common at 

 the time of fertilization and the remainder are added soon after. 



The sweet clover seed coat has almost cubical Malpighian cells 

 at the time of fertilization, with thin walls slightly thicker at the 

 outside. In six days the Malpighian cells begin to elongate and divide 

 so as to become very narrow. This elongation and division goes on 

 very rapidly for about eight days, when it appears that possibly the 

 :otal number of cells have been formed and that these get wider to 

 iccommodate the later growth of the seed. 



The cell walls begin to thicken soon after fertilization, and decided 

 thickening takes place on the outside at the time the cells elongate. 

 The domes begin to thicken in nine days and are completely formed 

 in about twenty days. The light line does not appear until the seed 

 is nearly mature. 



A very striking contrast is found between hard and soft seeds. 

 Hard seeds have their walls thickened so much below the light line 

 that the lumen extends only part of the way from the base to the 

 light line. In soft seeds a fairly large lumen extends to the light 

 line. This may allow larger pores to extend through the light line. 



The thickening of the cell walls of sweet clover and peas is similar 

 in that both are thickened in ridges leaving crevices between the vari- 

 ous thickened portions. The crevices are usually very narrow. 



In the garden pea the cell walls are generally thinner, especially 

 in young stages, than in sweet clover. The Malpighian cells change 

 very little for several days after fertilization. The remainder of the 

 cells of the integument enlarge very much. In about six days the 

 Malpighian cells elongate to several times their width and thicken a 

 very small amount. Thickenings come in very rapidly at the time 

 the seeds are nearly mature. 



The cells sometimes entirely close up due to thickenings, as in 

 the case of hard seeds. Seeds which are not hard usually have the 



