Resistance of the prothallia of Camptosorus rhizophyllus to 
desiccation * 
F. L. PIcKetr 
Camptosorus rhizophyllus (L.) Link is found growing with 
mosses and lichens on the shaded surface of dry limestone ledges 
and on detached limestone slabs in open ravines and torrent beds. 
Only rarely have groups been found in well-shaded or continually 
moist places in this region (southern Indiana). Growing in places 
thus exposed without constant water supply, the plants are 
subjected to brief periods of abundant moisture (during and 
immediately after precipitation) which alternate with longer 
periods of drought. That plants with a delicate prothallial stage 
in their life history could secure and retain residence under such 
conditions has been a cause for surprise. 
The drought-resisting power of some greenhouse cultures of 
this fern grown in the spring of 1912 suggested a possible adapta- 
tion to its well-known xerophytic habitat. In an attempt to 
‘determine lo what extent this ability to withstand drought might 
be a factor in adaptation, fronds with mature spores were collected 
in October, 1912, and cultures were made as usual on sterilized 
soil in clay saucers. These cultures were subjected to a variety of 
conditions to be later enumerated. 
An attempt was made to obtain information on the following 
points: the uniformity of spore germination and prothallial 
‘development, the ability of prothallia to resist or survive natural 
‘drought conditions, and the ability to survive conditions leading 
to complete desiccation. 
Fronds were collected on October 26, 1912, and kept between 
sheets of filter paper in a book in the laboratory. The sporangia 
were lightly crushed to free the spores and then sown on thoroughly 
sterilized soil, November 22, 1912. The cultures were kept in 
the greenhouse and were protected by bell-jars supported on 
* The writer has been unable to find any literature bearing upon this subject, 
for the prothallia of this or any other homosporous fern. 
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