258 PART III. — VEGETABLE PHYSIOLOGY. 



The second mode is by fertilization, or the union of two 

 distinct cells, one of which is usually of larger size and passive, 

 the germ cell ; and the other, smaller and commonly active, the 

 sperm cell. This mode is much the more common, and it exists 

 in many varieties. It is the only sexual mode observed in all the 

 higher types of plants. The description of its different modi- 

 fications is, however, reserved for Part IV, where they will be 

 treated of in detail in our study of the principal types of 

 plant life. 



There are few things in nature more wonderful than the re- 

 sults produced by fertilization. These, as we well know, are not 

 confined to the immediate effects upon the fertilized cell itself, 

 resulting, in the case of flowerless plants, in the production of 

 one or more spores, or in the case of flowering ones, in the devel- 

 opment of an embryo, each capable of giving rise to a new plant ; 

 but the effects reach to adjacent organs, and often modify them 

 in a profound manner. When Apple, Pumpkin or Melon blossoms 

 are fertilized, not only do the ovules undergo great changes of 

 structure and size, but the entire ovary walls undergo a very re- 

 markable development. In the Strawberry the influence extends 

 to the receptacle, and in the Checkerberry to the calyx, in each 

 case resulting in an extraordinary development of the organ. 



In the case of other organs the effect of fertilization may be 

 of the opposite character, namely, to cause their rapid withering 

 and decay, probably by a diversion of nutriment from them to 

 other parts. This is nearly always the case with the corolla, and 

 frequently also with the calyx, as every gardener knows, for if he 

 wishes to prevent, as long as possible, his flowers from withering, 

 he pinches off the anthers before they are ripe, or takes some 

 other means to prevent fertilization. 



How far these effects are the result, more or less remote, of the 

 stimulant effects of the fertilizing material on the germ-cell, and 

 how far they are due to the stimulant effects of the pollen-tube 

 on other tissues with which it comes in contact, is not yet known ; 

 but there are numerous facts to show that the effects cannot all 

 be due to the fertilization of the ovule. 



The Orchids, for example, show a very considerable develop- 

 ment of the ovary as a direct result of pollination, before the 

 pollen-tubes reach the ovules. There are good reasons, moreover, 



