484 F. L. PICKETT 
those found in nature in the growing season. Diffused light was 
secured by means of a muslin screen 2 m. above the culture tables or 
by means of a double layer of filter paper pasted to the bell jars and 
half covering them. As already found, the exposure of air-dry 
cultures to full sunlight during periods of three to five weeks proves 
fatal. Cultures exposed for nine weeks to normal dry air without 
water but shielded from the direct sunlight showed a few living plants. 
One of the cultures has been subjected to periods of drought one to 
two weeks in length during a total period of sixteen months, and has 
but rarely been watered twice in succession without an intervening 
dry period. Occasiorially it has been flooded, and has shown a new 
crop of sporophytes after each flooding. 25 per cent of the plants 
of this culture were living at the end of the sixteen months period, 
although they had undergone changes, as will be noted later. 
On December 8, 191 5, soil cultures with mature prothallia were 
placed outside the greenhouse, protected from direct sunlight by the 
building and an adjoining wall, and covered by bell jars. On March 26, 
1 9 14, cultures returned to the greenhouse showed all plants dead or 
injured. Injured plants had much the appearance of plants injured 
by too long exposure to drought, showing old dead tissue and groups 
of younger active marginal or meristematic cells. The lowest tem- 
perature to which these cultures were exposed was — 12° C. in this 
protected location, although temperatures around — 6° C. prevailed 
through January and February. 
Field Notes. — brief review of the weather conditions during the 
summer of 191 3 will give the field notes their full value. The summer 
was extremely dry and warm in southern Indiana. Following the 
flood period of March 23-27 with 9.2 in. of rain, April was much drier 
than usual. Then a period of 146 days, from April 30 to September 
12, showed but 35 showery days, with a total precipitation of but 6.3 
in. Between Sept. 13 and 30 there was a rainfall of 2.78 in., and then 
the drought continued up to Oct. 17, with but .48 in. in the interim. 
During the same period the following temperature conditions were 
recorded : 
Mean Maximum Maximum 
May 25.5° C. 35.' C. 
June 28.2 40. 
July. 344 41-9 
August 33.2 38.3 
Sept. 1-12 35- '38.^ • 
