480 THE BEAN PLANT. [CHAP. 



the two large fleshy cotyledons of the embryo will 

 be laid bare. Joining the cotyledons together 

 will be found the rest of the embryo : it consists 

 of a conical part (the radicle) lying outside the 

 cotyledons, with its apex directed towards the 

 point where the micropyle was : and of the rudi- 

 ments of the stem and leaves (plumule} lying 

 between the cotyledons. 



g. The process of fertilization. 



This is difficult to follow in the bean; but by using 

 different plants for the observation of its various stages 

 it is fairly easy to observe all its more important steps. 



1. A plant well adapted for seeing the penetration of 

 the pollen tube into the stigma and style is the 

 Evening Primrose (CEnothera biennis]. 



Detach the style from the flower and hold the 

 club-shaped stigma between the finger and thumb 

 of the left hand. Moisten it with a drop of water 

 and then make with a wetted razor several successive 

 cuts through it. This will divide the stigma into 

 several slices. Spread these out on a glass slide 

 with a needle in water and examine the thinnest, 

 after putting on a covering-glass. 



The triangular grains of pollen will be seen send- 

 mg out from one angle a tube into the stigmatic 

 tissue, which is easily seen from its slight difference 

 in colour. 



2. The entrance of the pollen-tube into the micropyle 

 can be readily made out in some species of Veronica. 

 The common V. serpyllifolia often to be found 

 in shady places on lawns is well adapted for the 

 purpose. A flower should be taken from which the 



