THE FjfurT AND THE SEED 



269 



Fig. 259. — Seed of 



the Bean: a. Radicle. 



b. Cotyledons. 



c. Plumule. 



The embryo is the young plant, consisting of a short stem 



{hypocotyl) with seed-leaves {cotyledons) and a minute bud {plumule) 



at its upp(?i' end, and a minute root {^radicle) 



at its lower end. The hypocotyl remains 



short in the Mango and in the Pea, but 



lengthens out in the French Bean, Horse gram, 



Castor, Cucumber, and many other seeds, 



wdien they germinate. The cotyledons may 



be thick and stored with plant-food (Horse 



gram. Bean), or thin (Castor). They may 



also be flat (Bean, Castor), or folded (Ipom^a). 



The number of the cotyledons marks two large classes of the 



ilowering plants, inz., the dicotyledons and the monocotyledons. 



In the monocotyledons the cotyledon has a 

 cylindrical shape sheathing the stem and its 

 bud, and developing at the side adjoining the 

 endosperm, of which we shall speak presently, 

 into a shield-like structure as in Maize, or 

 into a globular body as in the Cocoanut. 

 Here, as well as in many dicot^dedonous 

 plants, the cotyledons have the function of 

 absorbing a food-substance, which forms a 

 separate tissue within the seed coats, and 



that is the endosperm. (See germination of Castor seed, of Rice, 



and of Cocoanut.) Seeds containing endosperm are termed 



Fig. 260.— Endosperm 

 in the seed of Maize. 



Fig. 261.— Castor seed. 



endospermous, and those in wdiich endosperm is not present, 

 exendospermous. Exendospermous seeds have the food-substance 



