HOW PLANTS OBTAIN THEIR FOOD. 



103 



also hard and shining black, splits open at the opposite end, that 

 is at the stem end. It usually splits 

 open in the form of three ribs. 

 Next within the inner coat is a 

 very thin, whitish film (the remains 

 of the nucellus, and corresponding 

 to the perisperm) which shrivels up 

 and loosens from the white mass, 

 the endosperm, within. In the 

 castor-oil bean, then, the endosperm 

 is not all absorbed by the embryo 

 during the formation of the seed. 

 As the plant becomes 

 older we should note that 

 the fleshy endosperm be* 

 comes thinner and thin- 

 ner, and at 

 last there is 

 nothing but 



Fig. 93. 



How the garden bean comes out of the ground. First the looped hypocotyl, 

 then the cotyledons pulled out, next casting off the seed coat, last the plant erect, 

 bearing thick cotyledons, the expanding leaves, and the plumule between them. 



a thin, whitish film covering the green faces of the cotyledons. 

 The endosperm has been gradually absorbed by the germinat- 

 ing plant through its cotyledons and used for food. 



Arisaema triphyllum.* 



212. Germination of seeds of jack-in-the-pulpit. The ovaries 

 of jack-in-the-pulpit form large, bright red berries with a soft 

 pulp enclosing one to several large seeds. The seeds are oval in 

 form. Their germination is interesting, and illustrates one type 



* In lieu of Arisaema make a practical study of the pea. See paragraph 

 2i6a. 



