1902] 



CHANGE OF FORM IN PKOSERPINACA PALUSTRIS 



105 



# 



( 



V 



during these and other experiments during the day gave off Og 

 freely, and this could only occur when the cells are making 

 more than they can use and the protoplasm is supersaturated, 

 probably even more than in the air where the Og passes off with 

 less resistance; (2) because of the behavior in moist air where 



Fig. 10. — A plant whose upper leaves have developed in saturated air. 



the plants have the same amount of oxygen as usual in the 

 atmosphere. 



7- Moist air.— The water medium necessarily has the effect 

 of entirely checking transpiration, so that its passage from the 

 cells is entirely prevented, and the cells and protoplasm are filled 

 to their utmost capacity with water. This condition, to a certain 

 extent, can be imitated by growing the plants in an atmosphere 

 saturated with water vapor. Such a thing as a perfectly saturated 

 atmosphere, so far as the plant is concerned, is necessarily 

 impossible, for the temperature of the plant is always slightly 

 higher than that of the surrounding medium, and so evaporation 



