ELEMENTARY BIOLOGY. [CHAP. vin. 



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

 and the progress of the pollen-tube into the ovule 

 followed. 



3. The young fruit of Campanula (especially the com- 

 mon Canterbury Bells of gardens, Campanula me- 

 dia) is convenient for examining the embryo-sac. 

 It is only necessary to cut thin transverse sections 

 of the fruit and examine in water. Some of the 

 ovules cut through will allow the embryo-sac to be 

 seen, and in fortunate sections the embryo-vesicle 

 and the end of the pollen-tube in contact with the 

 embryo-sac. 



