ECOLOGICAL ADAPTATIONS OF CERTAIN FERN PROTHALLIA 489 
As an extreme trial a culture was watered October 8, 1913, and placed 
in full diffuse light with a temperature range of i2°-2i° C, in air not 
in contact with water surface or sprays. On October 10 the soil surface 
appeared dry. Small portions were removed for revival at intervals 
until March 28, 1914. At that time, after 171 days without water, 
20-25 per cent, of the plants were in condition for growth. 
Cultures allowed to become air dry in sunlight at a temperature 
range of 13-25° C. during January, February and March, showed 
about 50 per cent, of the plants living at the end of four weeks, and 
showed a few living plants after six weeks of such exposure. Weather 
conditions make great variations in the results of these experiments, 
and the above data must be taken as the average of many repeated 
experiments. It has been very interesting to watch cultures of A. 
platyneuron and C. rhizophyllus exposed to the same light conditions. 
The greater resistance of the former to combined light and drought is 
very noticeable. 
Winter Conditions. — Cultures placed outside on December 8, 1913, 
showed every plant living when brought inside on March 26, 1914. 
The lowest temperature to which these were exposed was — 12° C. 
and this seemed not to injure the plants in the least. This result 
was true with both dry and flooded cultures. Experiments to deter- 
mine the minimum temperature limit have not been arranged, but 
field observations have indicated that a temperature of — 23° C. is 
not necessarily fatal. 
Reaction to Special Light Conditions. — It has been stated above 
that the prothallia of ^. platyneuron grow well in direct sunlight, other 
conditions being favorable, and that they are less liable to injury 
than those of C. rhizophyllus v^hen cultures become dry in full light. 
It is now to be shown that they have a marked tendency to modify 
their growth as a result of variation in light intensity. 
Spores and crushed sporangia were sown on a modified Knop's 
solution in 6 cm. petri dishes and stender dishes. Check cultures were 
made on distilled water and sterilized tap water. The Knop's solution 
was prepared as follows: A. KNO3, 2 g.; MgS04, 2 g.; K2HPO4, 2 g.; 
Aq. dist., 2,000 cc. B. Ca(N03)2, 4 g.; Aq. dist., 3,000 cc. 
For use one part of A is added to three parts of B and boiled fifteen 
minutes. A series of check cultures was made with a solution similar 
to the above but with sterilized rain water instead of distilled water. 
No difference could be noted between the two series of cultures. 
