12 
NEIL E. STEVENS 
that the fungus continues to grow during mild periods of winter. 
During January, 191 3, an average lateral growth of 0.51 cm. was 
recorded for cankers at Charter Oak, Pa., while no growth whatever 
was recorded in November, December, or February. In this con- 
nection Anderson and Rankin call attention to the fact that during 
January there were ten different days in which a temperature above 
9° C. was recorded. As Rankin (9, p. 244) states, "cessation of growth 
of the mycelium in the bark during fall and winter as well as negative 
results of inoculations at this time of the year is explained purely on 
the basis that the temperature is too low for the vegetative activity 
of the fungus." 
Experiments made by the writer with plate cultures of Endothia 
parasitica in the laboratory agree with these field observations. When 
such cultures were kept at temperatures below their minimum for 
growth, that is, 7° C, 3° C, and 1° C, for twenty-four hours and 
then removed to room temperature for twenty-four hours, they grew 
practically as much while in the warm room as did cultures which had 
never been in the ice box. So quickly does the fungus recover from the 
effect of the low temperatures that plate cultures which were kept in the 
refrigerator for twenty-two hours and at room temperature for only two 
hours each day showed a measurable growth at the end of a week. 
Spring weather, with warm days and cool nights or even a warm period 
in midwinter would then permit growth. In fact plate cultures kept out 
doors at Washington, D. C, during January, 1915, made a total growth 
of 1 .5 cm. for the month. Anderson and Rankin further state (3, p. 575) 
that " the mycelium does not seem to be injured in the least by freezing, 
but remains alive in all parts of the canker during the winter. These 
investigators report that cultures kept frozen for a month at a time 
renewed growth naturalfy on being brought back into the laboratory." 
This being the case one would expect to find little connection 
between the length of frostless season and the amount of growth in 
the various localities. Table V gives the length of frost-free period 
in days during the time of the experiment at the various stations. 
There is of course in general a decrease in the length of frost-free 
period from Charlottesville northward. This is, however, not regular, 
since the length of frost-free period is greater at Hartford, Conn., than 
at Van Bibber or Woodstock, Md., while the growth is of course 
greater at the latter points. Williamstown, Mass., had a considerably 
shorter frost-free period than Hartford, Conn., and on the other hand 
