402 



BOTANY 



donous characters, and may perhaps be more nearly allied to the 

 Monocotyledons than to the Dicotyledons with which they have 



en- 



en 



FIG. 378. Types of dicotyledonous seeds. A, Peperomia subrotunda. B, Jeffersonia 

 diphylla. C, Diospyros Virginiana. D, Lamium album. E, Asclepias Cornuti. 

 en, endosperm; em, embryo; p, perisperm. 



usually been associated. It is possible that other anomalous Dicoty- 

 ledons e.g. Actsea, Thalictrum may show a similar condition. 

 There is usually a well-developed suspensor, 

 which may have its basal cell much enlarged, 

 as is so often the case among the lower 

 Monocotyledons. 



Cotyledons. The cotyledons may differ 

 but little from the later leaves, but usually 

 they are different in form (e.g. Ipomoea, Fig. 

 380), and may be thick and fleshy, in this 

 case not infrequently remaining permanently 

 within the seed. 



Germination (Fig. 379). When the embryo 

 is small, it grows until the surrounding endo- 

 sperm is nearly used up before the root 

 protrudes through the micropyle. In seeds 

 without endosperm, like the Horsechestnut 

 or Pea, the first evidence of germination is 

 the extrusion of the stout radicle, which at 

 once bends downward into the soil. In such 

 cases the thick cotyledons may remain within 

 the testa, or shell, of the seed, or they may be 

 withdrawn and develop chlorophyll, so as to 

 serve for photosynthesis, as well as for reservoirs of reserve-food. 



FIG. 379. Cucurbita 

 Pepo. Young seedling. 

 (After BAILEY.) 



