58 BOTANY OF CROP PLANTS 



Development of the Fruit. — The stimulus of fertilization, 

 which is not well understood, extends its influence not only 

 to the ovule, but to the ovary as well. Coincident with the 

 changes resulting in the mature seed, the ovary enlarges, and 

 its walls become changed both physically and chemically. 

 The ovary wall (pericarp) has three distinct layers. Named 

 in order from the outside to the inside, these are the exocarp, 

 mesocarp and endocarp. As the fruit develops the changes 

 that occur in these layers may differ. For example, in the 

 cherry or plum, the exocarp becomes the skin of the fruit, 

 the mesocarp becomes thick and juicy to form the fleshy 

 portion of the fruit, while the endocarp takes on a stony 

 character. 



Fruit and Seed Distinguished. — A fruit, botanically, is 

 the matured ovary, with its seeds, and any parts of the flower 

 which may be closely associated with it. The fruit contains 

 the seed or seeds. For example, the entire bean pod is a 

 fruit; the "beans" within are the seeds. It is in the case of 

 dry, one-seeded fruits, particularly, that distinction needs to 

 be made between fruit and seed. For example, the buck- 

 wheat fruit (achene) or grass fruit (grain) is commonly called 

 a "seed." But, if development of these is traced and their 

 structure carefully examined, they are seen to be true fruits, 

 with a very thin pericarp (ovary wall) enclosing one seed 

 (Figs. 35 and 115). 



Kinds of Fruits. — No attempt will be made at this place 

 to give a complete classification of fruits. We will describe 

 the different kinds as we meet with them in the discussions 

 of crop plants. Fruits with a dry pericarp, such as the grain, 

 achene, capsule and pod, are designated dry fruits. De- 

 hiscent dry fruits (capsule, pod, foUicle) split open at maturity 

 in a definite way permitting the seeds to escape. Inde- 

 hiscent dry fruits (achene, grain) do not split open at maturity 



