2l8 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D vSer. 



water is as unsatisfactory as though the sections were cut 

 from a moist thallus. 



The toughness of the thallus is due to the longitudinal 

 direction and the compact arrangement of the rather thick- 

 walled hyph^e near the surface. The surface is soft and 

 gelatinous when moist, hard when air-dry. The gelatinous 

 matter of the outer portions of the thallus both holds water 

 very strongly and takes it up very quickly. Air-dry at the 

 end of the long dry season, the lichen still contains 13.9 

 per cent, of water or nearly one-seventh of its weight, as 

 shown by the following figures : 



Weight air-dry 4.72 gr. 



Weight constant at. . 4.06 gr. when dried several 



hours at 90° C. 



Weight lost 0.66 gr. 



Percentage of water .13.9 



The dried lichen must be weighed quickly, for it rapidly 

 absorbs moisture from the air and returns to its original 

 weight. When absolutely dry it is as brittle as it ordinarily 

 is tough, and it may be ground in a mortar to a fine powder. 

 Microscopic examination' of this powder in water shows it 

 to consist of minute fragments of hyphas interspersed with 

 isolated gonidia apparently uninjured by the grinding. It 

 occurred to me to attempt drying the Hchen at a temperature 

 low enough to avoid injuring the gonidia. Warming in 

 an oven for five hours at 36° C. (96° Fahr.), a temperature 

 often attained, and sometimes maintained for several hours, 

 on a summer day, proved to be perfectly harmless to the 

 gonidia, but it did not dry the lichen to the point of brittle- 

 ness. To attain brittleness without further heating, small 

 pieces were kept for four days in a desiccator containing 

 glacial phosphoric acid. Even after this treatment the 

 fragments were not perfectly dry and brittle, though grind- 

 ing rapidly in a mortar yielded powder of which the finest 

 part contained isolated and apparently uninjured gonidia. 

 Some of this was inoculated by needle into hanging drops 

 of sterilized tap-water. 



