FERTILIZATION OF THE OVULES. 



283 



This function is often accomplished by Insects ; which, in going 

 from flower to flower in search of honey, cover over their bodies 

 with pollen-dust, and rub them accidentally against the pistils of 

 other flowers. When the pollen falls on the stigma, it is caused 

 to adhere to it by a honey-like secretion from its surface ; and 

 after a short time, it undergoes a remarkable change, which 

 closely resembles that already described in the spore of the 

 Cryptogamia. 



438. The outer coat of the pollen-cell appears to burst at 

 one or two points, and to allow the inner coat to pass out through 

 it in the form of a tube. This tube insinuates itself between 

 the cells of the stigma, and passes down between the long and 

 loosely-arranged cells of the style. It gradually extends, until 



FIG. 86. POLLEN-GRAIN, OF (ENO- 

 THERA BIKNNIS, sending its tubes 

 a, a, between the cells, 6, of the 

 stigma. 



it reaches the ovarium itself, even 

 when the style is several inches 

 long. The pollen-grains are not 

 always globular, but are some- 

 times triangular, and emit a pol- 

 len-tube at each corner, as in 

 Fig. 86 ; such are analogous to 

 the spores of Mosses, which put 

 forth several tubes. The tubes, when they arrive at the ovarium, 

 direct themselves towards its different chambers, and have been 

 seen to enter the apertures in the several ovules ; which are at 

 that time directed towards the part of the base of the style, from 



FIG. 85. SUCTION OF THB 

 TOP OF THE STYLE OF SNAP- 

 DRAGON ; showing the pas- 

 sage of the pollen-tubes 

 between its cells. 



