642 Pickett: RESISTANCE OF PROTHALLIA TO DESICCATION 
small blocks of wood to provide adequate ventilation. Some 
cultures were exposed to direct sunlight while others were exposed 
to strong diffused light only. The temperature conditions were 
the same, 20-25° C. The soil was kept moist, not wet, but was 
allowed to show a dry surface for a period of 12 to 24 hours once 
each week. The first green was noticed December 17, at which 
time the prothallia when examined with a microscope were found 
to be composed of two to ten cells each. These cultures showed 
good growth, seeming to suffer no injury from the dry periods. 
Those in the sunlight showed rather a more rapid development 
than those in diffused light. On February 11, 1913, the culture 
in sunlight contained prothallia in good condition but varying 
in size from merely germinated spores up to plants 2-3 mm. broad 
with but very few antheridia or archegonia. The culture in 
diffused light did not show similar prothallia until March 21, 1913. 
The spores of Camptosorus rhizophyllus germinate very irregu- 
larly. Twelve weeks after the spores were sown, a small bit of 
soil—not over 3 mm. square—removed from a culture where the 
plants seemed most thrifty, showed all stages in development from 
spores with the perinium just ruptured to prothallia bearing 
mature antheridia and archegonia. Many spores retain their 
vitality up to May in the dry atmosphere of the laboratory, and 
fronds collected in March furnished viable spores for cultures. 
The long dormant period of spores on the moist soil of cultures 
suggests that they might remain so on the soil of their habitat 
through the winter season. | 
Four methods of reducing water content were used. First, 
a glycerin desiccator was used, consisting of two glass vials 
through which, by means of an aspirator, a current of air was 
drawn after passing through two U-tubes containing glycerin and 
crumpled filter paper. Heaviest c.p. glycerin was used. The 
aspirator was arranged so that the air of the vials was changed 
about one hundred times each twenty-four hours. Second, cul- 
tures were left under bell-jars, exposed to the warm air and full 
sunlight of the greenhouse. Third, cultures were left under bell- 
jars, exposed to the dry air and diffused light of the greenhouse 
lobby or vestibule at a slightly lower temperature, 16-20° C 
This place represents as nearly as possible the natural growth 
