SEED-BEARING PLANTS 4^3 



403. Essentials of a Seed.— In the cycads and pines 

 we have seen accomplished the first step necessary for the 

 production of a true seed, namely, the retention within 

 the sporangium of the megaspore and the female gameto- 

 phyte to which it gives rise. The final step was the forma- 

 tion of an embryo, which usually rests before proceeding 

 to develop into an adult sporophyte. With few excep- 

 tions, the distinctive feature of a seed is a resting embryo. 

 The embryo may or may not be surrounded by nourish- 



FiG. 337— John Ray (1628-1 705). An early and noted English botanist. 

 First to distinguish monocotyledons from dicotyledons. 



ment stored in the form of endosperm. In the absence 

 of endosperm, as for example in the bean seed, the nour- 

 ishment is stored in the cells of the embryo itself, having 

 been absorbed while the embryo was forming. Enclosing 

 the other parts of a seed is the seed-coat which may be 

 derived from one integument (as in Pinus) , or from two 

 integuments organically united. These features are illus- 

 trated in Fig. 83. 



404. Monocotyledons and Dicotyledons. — Except in 

 rare cases, all plant-embryos possess either one or more 



