30 THE MICROSCOPE. 



be the fructifying substance. The development of 

 the pollen-grain after it has touched the soft viscid 

 tissue of the pistil is very remarkable ; one or more 



little processes bud 

 out of the grain (Fig. 

 13); in time this tube 

 or,'process becomes 

 much elongated (Fig. 

 14); it insinuates itself 

 between the cells of 

 the stigma, until, con- 

 tinually elongating it- 

 self, it arrives at the 

 ovule at the bottom 

 of the ovaries which 

 are thus fertilised by it. 

 The illustrations here 

 given will show these 

 changes in the pollen- 

 grain which we have 

 been considering. " In 

 tracing the origin and 

 early history of the 

 ovule, very thin sec- 

 tions should be made 

 through the flower- 

 bud, both vertically 

 and transversely ; but 

 when the ovule is large and distinct enough to 

 be separately examined, it should be placed on the 

 thumb-nail of the left hand, and very thin sec- 

 tions made with a sharp razor ; the ovule should 

 not be allowed to dry up, and the section should 

 be removed from the blade of the razor by a wetted 

 camel-hair pencil. The tracing downwards the 

 pollen tubes through the tissue of the style may be 



Fig. 14. 



Fig. 13. 



