88 



BOTANY. 



EXERCISE XXXVI. 

 Structure and Forms of Pollen. 



The pollen-grain is generally composed of two mem- 

 branes, or coats, filled with a thick liquid substance con- 

 taining minute grains, which is its essential portion. The 

 outer coat is frequently marked with bands, lines, and 



FIG. 



FIG. 255. 



FIG. 256. 



grooves, or covered with bristling points (Fig. 254). The 

 inner coat is very thin, and swells when wet. If you 

 moisten pollen-grains, you may often see, with a micro- 

 scope, the expanded inner coat protruding through open- 

 ings in the outer coat. 



EXTINE. The outer coat of a pollen-grain, usually 

 with openings, or very thin in certain places (Figs. 254 

 and 255). 



- Fovilla. 



Intine 



Exline. 



FIG. 257. 



FIG. 258. Pollinia. 



FIG. 260. 



INTINE. The inner coat of a pollen-grain, very thin, 

 tough, and elastic, often seen protruding through holes in 

 the extine (Figs. 255 and 256). 



