764 PHTSIOLOGT. 



circumstances, plants make their appearance, which present 

 characters of an intermediate nature between two known species. 



3. Of the Eruit. — When the process of fertilization has 

 been effected in the ovule, as already noticed (see p. 297), 

 important changes take place in the walls of the ovary and the 

 surrounding organs of the flower, the result of which is the for- 

 mation of the fruit. The calyx and corolla generally fall off, 

 or if persistent, do not form any portion of the fruit, except when 

 the calyx is adherent, as in the Apple {fig. 702), when it neces- 

 sarily constitutes a part of the pericarp ; the style and stigma 

 also become dry, and either fall off, or are persistent, as in 

 the Poppy {fig. 428), and Anemone {fig. 684). The principal 

 changes, however, take place in the wall of the ovary, which 

 usually becomes more or less swollen, and soon undergoes im- 

 portant chemical changes, and forms the pericarp, either by itself, 

 or combined with the adherent calyx. Some pericarps, as al- 

 ready noticed (p. 300), are fully developed Avithout the fer- 

 tilization of the ovule, as those of many Oranges, Grapes, 

 Bananas, &c. The fruits thus formed, although frequently 

 more valuable than others for food, &c. , are useless for reproduction. 



The fruit in its growth attracts the food necessary for that 

 purpose from the surrounding parts, hence, the fruiting of 

 plants requires for its successful accomplishment an accumula- 

 tion of nutrient matter, and is necessarily an exhaustive process. 

 That the reproductive processes, and especially the maturation 

 of the pericarp, tends to exhaust the individual, is proved in 

 various ways. Thus, plants are annual, as already noticed 

 (p. 126), when they fruit the same year in which they are 

 developed from the exhaustion of nutrient matter thus occa- 

 sioned ; and that such is the reason is proved by the fact, that 

 we can make annuals, biennial or even perennial, by plucking 

 off the flower-buds as they are developed, and thus enabling 

 them to produce wood, &c. Again, a bad fruit year is generally 

 succeeded by a good one, and vice versa, because in the former 

 case an additional supply of nutrient matter is stored up for the 

 fruiting season, and in the latter there is a diminished amount. 

 Again, if a branch of an unproductive tree have a ring of bark 

 removed so as to prevent the downward flow of the elaborated 

 sap, its accumulation above will cause the branch to bear much 

 fruit. Pruning depends for its success upon similar principles. 

 In order to obtain good fruit it is also necessary, not to allow too 

 many to come to perfection on the same plant. Other matters 

 connected with this exhaustion by fruiting have been already 

 alluded to, in speaking of Annual, Biennial, and Perennial 

 Roots, at page 126. 



The changes produced upon the atmosphere in the maturation 

 or ripening of the fruit, depend upon the nature of the pericarp. 

 Thus, when tlic pericarp preserves its green state, and always 



