LABORATORY WORK 227 



contents of the testis may be pressed out into 0.9 per cent, sodium 

 chloride. 



The Structure of a Flower 



Examine a buttercup or other large regular flower. Note 

 the four sets of organs : 



1. The outer green calyx, which formed the covering of the 



flower in bud. 



2. The corolla, consisting of petals, the most conspicuous 



part of the flower, usually coloured. 



3. The stamens or male elements. Each consisting of a 



stalk we filament, ending in a knob, the anther. Tease 

 an anther in water and examine with the microscope. 

 Note the pollen grains. 



4. The/w/*/, consisting of separate carpels in the buttercup. 



At their upper ends they have a sticky surface, the 

 stigma ; in the interior of the lower part, the ovary, 

 will be found the ovules. 



Process of Fertilisation in the Plant 



This is difficult to follow in all its stages in one species of plant. 



^^penetration of the pollen tube into the stigma and style can 

 be seen in the evening primrose. 



Hold the stigma and style between the finger and thumb of the 

 left hand. Moisten with a drop of water and cut successive 

 sections with a razor, wetted with water. Spread them out in 

 water with a needle and examine with a low power. The 

 triangular pollen grains send out a tube from one angle into the 

 tissue of the stigma. 



The entrance of the pollen tube into the ovule can be made out 

 in yeronica serpyllifolia, the speedwell, common in meadows. 



Take a flower from which the corolla has just dropped. Dissect 

 out the small ovary, and open one of its two chambers with needles 

 in a drop of water. The use of a lens may be necessary. A mass 

 of ovules is removed from the interior and teased apart. Put on a 

 cover-glass and search for an ovule showing the entrance of the 

 pollen tube. The further progress of the pollen tube can be seen 

 better if dilute glycerine be run under the cover-glass and allowed 

 to soak into the ovule and make it transparent. 



