120 STRUCTURE OF THE SEED 



with the embryo (Fig. 82, B). The integument also undergoes 

 various changes during these growths, often becoming hard or pa- 

 pery or provided with hairs, hooks, spines, and smooth or pitted. 

 Compare the bean, catalpa, cotton, milkweed, etc. Attention 

 must also be directed to the growths that occur outside of the 

 seed that are induced by fertilization and the germination of the 

 gametospore. Very frequently the pistil becomes tough and 

 hard and invests the seed like a second integument, as in wheat, 

 corn, acorn, etc; again it forms a sac about the seed as in the 

 sedges and buttercups; or it may enlarge, forming the pods of 

 peas and beans or the capsules of lilies. In other cases it be- 

 comes fleshy throughout as in the tomato and currant, or only 

 the outer walls are fleshy while the inner part forms the pit or 

 stone as in the peach and plum. Frequently wings and hooks 

 grow out from the pistil as in the maple, Ailanthus, etc. Even 

 the end of the stem, the receptacle, which bears the various 

 organs of the flower, may be induced to grow, as in the apple, 

 where it surrounds the pistils (the core) with a fleshy coat, or 

 the receptacle may enlarge, as in the strawberry, forming the 

 fleshy part of the fruit. In other cases outgrowths below the 

 flower develop, forming the burr of the chestnut, clotbur, beech- 

 nut, and the cup of the acorn. The entire growth that is asso- 

 ciated with the formation of the seed is termed the fruit and we 

 see that it may include a variety of modified organs. The term 

 seed, however, refers only to the modified ovule and its embryo. 

 Later in the work it will be noted that these growths are often 

 devices to bring about a distribution of the seed or to protect it 

 during its dormant period. 



55. The Seed and its Growth. — Spores of all kinds germinate 

 and produce new plants. Seeds do not germinate. They simply 

 continue the growth of the embryo or plant which has been tem- 

 porarily stopped. The falsely called germination of the seed is 

 but the awakening or renewal of the growth of this plant. The 

 seed is essentially a young plant that is supplied with a certain 

 amount of food and that has temporarily stopped growing. 

 The seed may be looked upon as one of the many adaptations 

 found among plants to ensure their perpetuation. From a seed 



