PICKETT: A STUDY OF CHEILANTHES GRACILLIMA 335 
become entirely dry after April 1, 1922. This condition con- 
tinued up to July 31, 1922, when one of the cultures was moist- 
ened from below. The plants in this culture showed complete 
recovery the following day. This culture was not moistened 
again until November 6, when it again showed complete re- 
covery. On September 21, a second culture which had received 
no water since April I was moistened from below and on the 
following day this culture showed complete recovery. From 
these experiments it was evident that the prothallia of this plant 
were able to withstand very unusual drought conditions. Steps 
were taken to determine more fully their ability to survive such 
treatment. On November 7, portions of soil bearing prothallia 
were taken from a culture, which had not been moistened 
since April 1, and placed in two desiccators, one containing an- 
hydrous calcium chloride and the other anhydrous phosphoric 
acid (sticks). From time to time shall portions of these cultures 
were removed and were moistened by placing them upon moist 
filter paper. For a considerable time this was repeated in forty- 
eight hour periods until it became evident that the extreme desic- 
cation was doing but little damage, after which the periods were 
lengthened. On January 29 the last portion of these cultures 
was removed. Its plants showed almost complete recovery 
within a few hours after being moistened. These prothallia had 
thus survived exposure to absolute drought for a period of thir- 
teen weeks. We have no reason to believe any moisture could 
have reached them in any way during that time. The soil 
on which they were growing was a small cake, perhaps 10 sq. 
cm. in total extent in the beginning and at no place exceeding 
5 mm. in thickness; moreover, this soil was taken from a culture 
which had been exposed to normal dry atmosphere through a 
period of seven months before being placed in the desiccator. 
The same type of apparatus was used as described above, and 
the same precautions observed to prevent entrance of invalidating 
factors. 
Final proof of the survival of plants was made by placing 
them under normal conditions of growth for a considerable 
period. In every case where they have been reported as surviv- 
ing the desiccation, they continued to grow and even produced 
sporophytes. In the case of plants which had already produced 
rophytes before being placed in extreme conditions it was 
ai that prothallia and sporophytes survived equally well. 
