336 PickETT: A STUDY OF CHEILANTHES GRACILLIMA 
As in the case of spores, so prothallia and young sporophytes | 
show no evidence of ability to resist desiccation. Vigorous 
plants on moist soil when exposed to the warm, dry atmosphere 
of a class room were completely wilted in thirty to forty minutes. 
The peculiar characteristic of this, as of other ferns studied by 
the writer, seems to be the ability to survive the actual loss of 
water far below the percentage usually considered essential to 
the preservation of life. 
As far as the writer has been able to find there is no previous 
record of the survival of such extreme desiccation by fern pro- 
thallia or sporophytes. Attention has already been called to the 
importance of such ability to survive difficult conditions in the 
preservation of two other species of ferns, Camptosorus rhizo- 
phyllus, and Asplenium platyneuron. No doubt, in the case of 
C. gracillima, this peculiarity is an important factor, if not 
indeed the most important, in making possible the growth of 
this fern on the buttes of southeastern Washington, and in the 
even more arid regions in the southern portion of its range. 
In December, 1922, experiments were carried on to determine 
the ability of these prothallia to withstand low temperatures. 
Dry prothallia were uninjured by an exposure of two weeks to 
temperatures ranging from 35° F. to — 10° F. Cultures of 
vigorous growing plants on moist soil showed considerable 
injury through exposure to the same conditions, although a few 
plants survived. The finding of a small number of prothallia 
on Kamiak Butte in April, 1923, prothallia too large to have 
developed this year, is evidence that they do survive the winter- 
conditions in this locality. 
emingly closely connected with the hardy qualities of 
other ferns studied, is the tendency to develop outgrowths on 
old prothallia. This form of vegetative propagation is com- 
monly found in old cultures of C. gracillima. As already men- 
tioned various marginal or submarginal groups of cells, in no 
way related to the apical sinus or group, renew their meristematic 
characteristics and produce various forms of outgrowths. This 
tendency is more strongly developed in C. gracillima than in 
other forms studied. Fics. 26, 27 and 28 show margins almost 
wholly given over to this peculiar growth. In old cultures 
prothallia sometimes show a marked crenulate and ruff 
appearance produced by the abundance of these outgrowths. 
