644 PiIcKETT: RESISTANCE OF PROTHALLIA TO DESICCATION 
Results—sulphuric acid desiccator.—A portion of soil bearing 
prothallia was removed to a porcelain dish in a desiccator con- 
taining c.p. sulphuric acid. The lid was sealed down with vaseline 
and the apparatus placed in diffused light at a temperature of 
16-20° C. After eighteen hours the prothallia showed a marked 
yellowish color. A portion removed after four days showed a 
recovery of but two or three per cent. The plants removed at 
this time recovered very slowly, requiring a week to resume a 
normal appearance. 
Results—normal dry air.—The soil mass of a culture was divided 
into two approximately equal parts and carefully removed to 
sterilized clay saucers. One portion was placed under a bell-jar_ 
exposed to the full sunlight in the greenhouse. The other was 
kept under a bell-jar exposed to full diffused light and at a temper- 
ature of 16-20° C., an average of four degrees lower than that for 
the first portion. After three weeks, but a few of the plants 
exposed to direct sunlight recovered, and all were dead after five 
weeks of such exposure. Of the second lot not exposed to direct 
sunlight a portion removed after thirty-four days showed almost 
complete recovery. After fifty-five days, about 25 per cent of the 
prothallia recovered. After sixty-three days, a very few of the 
largest plants recovered and continued to grow. 
The conditions under which the second group of plants was 
kept approximate very closely the summer conditions in the 
regular habitat of Camptosorus rhizophyllus. The results of that 
set of experiments certainly suggest an explanation of this plant’s 
abundant growth under such conditions. It should be noted here, 
as above, that full recovery of the plants has been demonstrated 
by their continued growth and later production of sporophytes. 
If mature prothallia can withstand continuous drought for two 
months, they would certainly survive the difficulties of the 
average season after late March, at which time spores may 
germinate outside. The occasional rains through the summer 
would make possible recovery, fertilization, and the coguape of 
sporophytes. 
In connection with this set of experiments another should be 
noticed. A culture was prepared as for all the above on No- 
vember 25, 1912. The drainage was such that a part of the soil 
