THE WATER llEACTION IN A LIVERWORT 263 



although not so long, are possibly more intensely arid than the 

 dry season in the portion of California to which reference is made. 

 The response of a liverwort to the more arid desert region, there- 

 fore, has an especial interest. 



THE HABITAT AND HABIT OF PLAGIOCHASMA' 



No liverworts have been reported from the domain of the 

 Desert Laboratory, which is probably too arid for these forms, 

 but one species, Plagiochasma sp., was found by the writer on the 

 southern face of the Santa Catalina mountains at an altitude 

 of approximately 5000 feet. The rainfall at the altitude is 18-22 

 inches and occurs periodically, being about equally divided in 

 amount between winter and summer. At the time when the liver- 

 wort was seen, October, there was no rain but the humidity was 

 probably not so low as in the foresummer. It was mainly for this 

 reason that the species was fully expanded, although there was the 

 additional one that it was growing in a protected situation among 

 some mosses at the northern base of a cliff. 



Material of the liverwort was brought in the active condition 

 to the glass house of the Desert Laboratory. It was given water 

 frequently through the winter and remained fully expanded. 

 Early in the following spring the plants were somewhat neglected, 

 water was not given for a few days, and they promptly rolled up, 

 losing their characteristic color and form, becoming as lumps 

 of the soil on which they were resting. Upon being given water, 

 however, they expanded within a few minutes and assumed their 

 familiar appearance.^ 



When opportunity offered, some experiments were made on 

 the liverwort for the purpose of learning the amount of water 

 lost on drying. Separate thalli were removed from the group of 

 plants, the soil particles were brushed away, and the moist weight 

 was determined. Afterward, when the thalli had become air-dry 

 and had assumed the appearance described above, the weight 



^ The determination of the liverwort was by the kindness of Prof. A. W. Evans. 

 ^ See, also, Resistance of drought by liverworts, D. H. Campbell, Torreya, 

 4. 1904. 



