124 BOTANICAL GAZETTE [avucust 
upon a certain balance between the amount of water taken up and 
transpiration, then a variation in the moisture of the atmosphere 
would have an effect on fertilization. 
The comparative potency of pollen in self and cross- 
pollination 
Polien tubes can be traced through the stylar canal by mount- 
ing the pistils in a 30 per cent sucrose solution and flattening with 
a little pressure on the 
cover glass. The tubes 
have a denser and more 
granular content than the 
cells of the style and these 
features make it possible 
to trace them. Sufficient 
pressure causes the ovary 
to break just above the 
ovules and enables one to 
see the tubes in the ovary. 
Fig. 1 shows the upper 
portion of an ovary with 
exposed pollen tubes 55 
hours after — pollination. 
For self and cross- 
pollination vigorous field 
plants were selected, and 
flowers to be used were 
put under cover 2 oF 3 

Fic. 1.—Camera drawing, showing the upper : 
Portion of an ovary teased off and the pollen tubes days previous to opening 
invading the Ovary. and remained covered 
mo until collected for examl- 
ation. Flowers were self-pollinated by simply springing the keel. 
me cross-pollination the keel was sprung, and the pollen collected 
ners er plant was applied to the stigma with a scalpel. An 
examination of 30 flowers crossed showed the pollen tubes in the 
ovary 50 hours after pollination. Sections of ovaries killed 55 hours 
aiter crossing showed that the egg had enlarged for its first division 

