PLANTAGO-CLAYTONIA 69 



far as the seed is concerned, why the cotyledons should not lie 

 in the usual position. 



It has occurred to me that perhaps the arrangement of 

 the cotyledons may have reference to their exit from the seed. 

 If we examine a germinating seedling of Claytonia, we shall 

 see that the testa splits vertically from the micropyle, and the 



FIG. 114. Claytonia perfoliata. A, transverse section of seed, x 15. 

 B, seedling, x 6. 



cotyledons from their position, when they separate, act with 

 greater advantage in enlarging the orifice, and thus securing 

 their exit, than they would if they occupied the more usual 

 position. This, however, I only throw out as a suggestion 

 which requires further investigation. 



When the seed is flattened laterally, the embryo must 

 either be narrow or lie with 

 the edges of its cotyledons 

 to the placenta. 



For instance, in Helio- 

 phila pilosa var. incisa the 

 seeds (fig. 115, A and B) 

 agree closely in form with 

 those of Cheiranthus (C. 

 Cheiri) (figs. 73 and 74); 

 they are oblong-obtuse at 

 each end, compressed dor- 

 sally, with a notch at one end, and in section are narrow elliptic ; 

 but while the cotyledons of Cheiranthus are broad, in Heliophila 

 they are long and linear. The reason of this may be that while 



FIG. 115. Heliophila 

 dinal section of 



ilosa. A, longitu- 

 x 12. B trans- 



verse section of seed, x 12. 



