The Living Materials 47 



embryo at the time the seeds are "ripe" (Johnson, 

 1912, 444). (Figs. 14, 15.) It is, therefore, pos- 

 sible to cut an embryo into bits and grow any one 

 of these fragments. But, as Smith (1907, 325), 

 Molliard (1921, 106), LaRue (1936, 82, 104), Dau- 

 phine (1929, 94), and others have shown, even in 

 the embryo there are some regions having a 

 greater proliferative capacity than others, an ob- 

 servation which agrees with that established in 

 animal embryology. Cotyledons will usually re- 

 generate easily (Molliard, 1921, 106; Behre, 1929, 

 275). Roots can be counted on to grow as roots, 

 but means of inducing them to develop leaves 

 have, with rare exceptions (especially among the 

 Compositae) (Fig. 16), not yet been found. 

 Hypocotyl is in general still more refractory, 



E< 



Fig. 15. Detail of endosperm and embryo of Peperomia hispi- 

 dula. This is an ideal type of material for the study of embryo 

 differentiation after germination. (From Johnson, D. S. 1914. 

 Am. J. Bot. 1: 396, fig. 110, 444.) 



