92 STUDY OF COMMON PLANTS. 



REVIEW AND SUMMARY. 



After the process of fertilization has taken place, re- 

 markable changes occur aside from those of the ovule 

 Development already described. The corolla withers, and 

 of the fruit, the ovary increases in size, finally becoming the 

 fruit, which in ordinary cases is to be thought of simply as 

 the ripened ovary. In some species, however, the calyx- 

 tube forms a part of the fruit, and still other exceptional 

 forms of developmental history occur. The wall of the 

 ovary, which becomes the' pericarp, generally changes in 

 texture, becoming firm and leathery as in the bean, or 

 fleshy as in the cucumber, or partly fleshy and partly bony 

 as in the cherry, and so on. The pericarp often shows 

 three fairly distinct layers corresponding to the upper and 

 lower epidermis and intervening parenchyma of the car- 

 pellary leaf, the outer layer being known as the exocarp, 

 the middle, mesocarp, and the inner, endocarp. Thus, in 

 the peach, the skin is the exocarp, the fleshy part the 

 mesocarp, and the stone the endocarp. In the pod of a 

 bean or pea, the correspondence between the parts of the 

 pericarp and those of the carpellary leaf is still more 

 manifest. In many other fruits the changes that have 

 occurred render this relation less easily observed, and are 

 frequently still more fundamental in character. In some 

 cases in which the ovary is composed of several carpels, 

 only one develops, the rest becoming abortive ; in others 

 the ovary becomes divided by one or more septa, which 

 give the fruit the appearance of having arisen from a com- 

 pound pistil with more than the actual number of carpels. 

 These and other important features of the developmental 

 history of fruits are best understood by a careful com- 

 parison of their structure in different stages of growth 

 from the pistil to the mature condition. 



