264 W. A. CANNON 



was again determined. Finally the air-dry plants were allowed to 

 absorb water freely, when the plant was again weighed. The two 

 following tables report typical results with separate thalli. 



Experiment I 



Weight of moist plant .0367 gr. 



Weight of air-dry plant .0085 gr. 



Percentage of water lost to weight of moist plant 76 



Experiment II 



Weight of moist plant .0499 gr. 



Weight of dry-air plant .0147 gr. 



Percentage of water lost to weight of moist jjlant 70 



For the purpose of learning how much the same plants would 

 absorb they were given water, and after having become air-dry, the 

 superficial water was removed, as much as possible, with blotting 

 papers. In addition to this the plants were permitted to remain 

 in the dry room-air for a few moments. The thalli absorbed water 

 at once and assumed their customary color and form. Upon 

 being weighed again it was learned that the plant used in the 

 first experiment had gained 38 mgm., or 10 mgm. more than it 

 had lost on becoming air-dry. The thallus of the second experi- 

 ment gained 50 mgm., or 15 mgm. more than it had lost by dry- 

 ing out. 



The experiment was repeated with several thalli together for 

 the purpose of making less the probable errors which were un- 

 avoidable when single thalli were employed. The results, in 

 tabulated form, are as follows : 



Experiment III 



Weight of moist plants 1 048 gr. 



Weight of dry-air plants^ .203 gr. 



Amount of water lost .845 gr. 



Percentage of water lost to weight of moist plants 80 



The thalli used in the last experiment were returned to the 

 glass house and were left for twenty-five days, or until May 23, 

 without having been given water. During this period the humid- 



^ After weighing, the moist plants were allowed to become air-dry by standing 

 exposed for twenty hours in a dry, warm room. 



