178 



STRUCTURAL BOTANY 



in a slightly different way from that in Dicotyledons, 

 is shown in Fig. 79. 1 



In the pollen-grain itself further changes take 

 place. The nucleus divides, and around one of the 

 two nuclei thus produced a small cell is formed 

 (see Fig. 80,0). 



This, as in the Wallflower, is the generative cell, so 

 called because it is directly concerned in fertilisation. 

 It is much more easily seen in the 

 large pollen-grain of a Lily than 

 in the small one of a Wallflower. 

 The membrane of the ripe pollen- 

 grain is cuticularised, and its sur- 

 face is rough, with raised ridges, 

 which form a delicate network. 

 Along one side of the grain there 

 is a fold, the membrane of which 

 is thicker than the rest of the 

 wall; it is smooth, and consists 

 of pure cellulose. In the contents 

 of the grain there are many starch 

 granules. 



of the anther takes place as 

 described in the Wallflower. Here also the wall 

 separating the two pollen-sacs on the same side of the 

 anther breaks down at the moment of dehiscence (see 

 Fig. 40, of Wallflower, p. 1 1 1), so that the perfectly ripe 

 anther appears to have only two compartments instead 

 of four. The abundant pollen is set free, but most of 



1 For the whole development of the stamen careful reference must be 

 made to the description given in the case of the Wallflower (pp. 109-114). 



FIG. 80. Pollen -grain 

 of Lily at the begin 

 ing of germination. 

 g, small generative 

 cell with its nucleus ; 

 p.t, first outgrowth 

 of pollen-tube. Oil 

 drops are shown out- 

 side the grain. Mag- 

 n ified several hund red 

 times. (After Dodel- 

 Port.) 



The dehiscence 



