XVI.] THE BEAN PLANT. 481 



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 

 that after some time the embryo-sac can be seen, 

 and the progress of the pollen-tube into the ovule 

 followed. 



3. In favourable median sections of the ovule of the lily 

 prepared as directed in e. 5. c. e., the pollen-tube may be 

 traced through the micropyle and between the cells 

 of the nucellus to the embryo-sac. 



4. Among other plants favourable for the study of the 

 details of fertilization may be mentioned Caltha (marsh- 

 marigold), Helleborus, and Campanula (Canterbury 

 Bells). In each case thin transverse sections of the 

 fruit are to be made, and the material is best prepared 

 as above described. 



M. 31 



