ECOLOGICAL ADAPTATIONS OF CERTAIN FERN PROTHALLIA 483 
These results agree very closely with those secured with the closed 
desiccators as formerly reported (Pickett, '13), the slight discrepancy 
being accounted for by the use of larger and older plants in the present 
work. They also clear up the discrepancy between the results with 
the glycerine desiccator and the sulphuric acid desiccator as previously 
reported, and give an important check to the value of the three agents 
used in drying currents of air. While not quite as striking as earlier 
results, in view of the extreme conditions, they are worthy of con- 
sideration. This becomes more evident if the data be compared with 
the following from non-resistant forms. Prothallia of Onoclea struthi- 
opteris, Dryopteris stipularis and D. mollis used in check experiments 
have been killed by allowing soil of cultures to be dry for 2 days in 
sunlight, and can withstand but 2-3 hours exposure in the desiccator. 
It may well be noted here that several times small plants, bearing 
10-15 leaves, of Polytrichum piliferum were placed in the drying tube 
with the fern prothallia and recovered completely although left 3-5 
days after the prothallia were dead. Small plants of an unknown 
Bryum survived similar exposure without damage. This is taken to 
show that injurious gases were not present in harmful quantities, 
if at all. 
Cultures for experimental work were regularly made by sowing 
free spores and crushed sporangia on rich loam in 12 cm. unglazed 
clay saucers with perforated bottoms. These saucers were placed 
in others 18 cm. in diameter. Irrigation was controlled by supplying 
water as needed to the outer saucer. Both saucers and soil were 
sterilized 1.5-2 hrs, at a temperature of 130° C. in an autoclave each 
day for three days before the spores were sown. The cultures were 
covered with tall bell jars with one side raised by a cork i cm. high to 
provide ventilation. As has been already reported (Pickett, 1914) 
cultures of this fern do not show uniform development. Some spores 
germinate in ten days or less, and by rapid growth produce sexually 
mature plants in ten to twelve weeks. Other plants develop slowly, 
and some spores lie dormant for three to four months under conditions 
suitable for germination. Numerous cultures have been made from 
spores of fronds collected in the field in March and April, a clear proof 
that some spores even live through the winter. 
Extreme Natural Conditions, Experimental. — Cultures of mature 
plants were exposed to long dry periods in full sunlight and in full 
diffused light in the greenhouse, the conditions being approximately 
