FERTILIZATION 121 



to be good material for showing pollen-tubes. Cut transverse 

 sections of the style in the fresh state, mount in dilute glycerine 

 and observe 



1. The tissue of the style with small vascular bundles dotted 

 in it. 



2. The star-shaped central cavity, filled with mucilage, 

 embedded in which may be seen 



3. The small pollen-tubes cut transversely, and embedded 

 in a mass of transparent mucilage. 



Cut longitudinal sections of the same, including the stigma, 

 and mount as before : observe 



1. The irregular stigmatic surface. 



2. The numerous pollen-grains (associated in groups of 

 four) attached to the stigma, and often putting out pollen-tubes 

 which penetrate the tissue of the style. 



3. The pollen-tubes, often to be seen as a dense sheaf, 

 pursuing their course down the cavity of the style : note their 

 thin walls, and the presence of highly refractive plugs, which, 

 stop their cavities : look for endings of the tubes, in which the 

 protoplasm will be denser, and one or two nuclei may be 

 observed there. 



IV. Pick out gently a number of ovules from an ovary of a 

 flower of Datura Stramonium, or of Digitalis purpurca, which 

 has just faded, and mount in dilute glycerine. Observe 



1 . The campy lotropous ovules, with curved body. 



2. Pollen-tubes, which are often to be found with the end 

 applied closely to the micropyle. 



Similar observations may also be made on Stellaria media, 

 and many other plants. 



RESULTS OF FERTILIZATION. 



A. DEVELOPMENT OF THE EMBRYO. 



i. Dicotyledon, 



Pick out the ovules from a fresh ovary of Capsella Bursa- 

 pastoriS) which has attained about half the ultimate size of the 

 mature fruit : material kept in spirit will not do well for this 



