VIIL] THE BEAN-PLANT. 87 



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 ((Enothera 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- 

 ing 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 

 corolla has just dropped. Dissect out the minute 

 ovary and, using the dissecting microscope, open 

 with a needle one of its two cells in a drop of water ; 

 remove the mass of ovules and gently tease them 

 apart. Then put on a covering-glass and examine 

 with a low power till an ovule is found which shews 

 the entry of the pollen-tube. The addition of dilute 

 glycerine will make the ovule more transparent, so 



