[Chap. XXXII 



FLOWERS, FRUITS, AND SEEDS 



367 



Fig. 163. Pineapples in Hawaii. The entire flower cluster ot each plant becomes a 

 compact multiple fruit. Photo from U. S. Forest Service. 



The seed. We have already seen that the ovulary contains ovules, 

 which ultimately become seeds. Seeds are unlike in size, foim, composi- 

 tion, and in several other wavs. The seeds of some orchids are almost 

 microscopic in size, while those of a few tropical legumes and of certain 

 nut-bearing trees mav be several inches in diameter. From a study of a 

 few kinds of seeds one mav learn to recognize their essential parts. 



The seed coats of the castor bean, for example, consist of a hard outer 

 layer and a thin paper v inner membrane. The seed coats enclose the 

 endosperm and the embryo. The embryo is the young plant of another 

 generation of castor bean. It consists of a very short stalk {hypocotyl) 

 and two thin, colorless leaves, or cotijledons. Between the bases of the 

 two cotvledons is a bud — the plumule — from which the stems and 

 leaves of the seedling de\'elop. No root is visible in the embryo; but 

 when the seed germinates, the basal tip of the hypocotyl elongates, and 

 from its root primordium a primary root develops. The seedling that 

 develops from the embryo of a germinating seed is at first dependent 

 upon the food which accumulated in the cells of the embryo and endo- 

 sperm while thev were developing in the seed. 



The seed of the kidney bean differs from that of the castor bean in the 

 absence of an endosperm. It consists only of an embryo enclosed by 



