ENpDoTHIA CANKER OF CHESTNUT 575 
TABLE 5. AVERAGE Rate or GrowtH oF CaNnKERS DuRING SUMMER MONTHS, 
AT NAPANOcH, NEw York 
Number Growth by periods of four weeks 
: : of (in centimeters) 
Date when inoculations ak 
were made ae eel 
May June july August | September 
Mayi2: vs sat enienes teas 60 1.35 1.75 3.0 2.4 23 
JUNE Tocca eater es BBi: | orden aiers 2.5 1.72 BuO || aranee-s 
June! Bi sis se occasion sane 1G) sxeges lt a geeen 2.0 TAQ’ | saves d 
July 3G eve weed Al | sdeiic: [eves Te75t | waseeu | Seca eees 
July ssi ces TOS: |ioaceeec.. | ohana 2.0 17 17. 
August 1........ gyaeists Dude | ibessontotacth tls tite Miceceak crear aes 7 a ree 
Average coccetei call socaias 1.35 2.08 2.1 2.2 1.9 
of the canker around the tree, the increase in length being considered 
not so important. It appears that the mycelium continues to grow even 
during mild periods of the winter, such as were = during January 
of 1913. 
As a check on the above data, agar plate cultures were kept out during 
the winter and growth was recorded during each warm period. In this 
connection, Shear and Stevens (1913a:9) note that the minimum tem- 
perature for growth of the fungus in culture is 9° C. (48° F.), which tem- 
perature was exceeded on ten different days during January. 
Even the most rapid growth, as recorded above for the summer months, 
is less than one millimeter a day. But on artificial media a, growth of 
three millimeters a day is not unusual. Mycelium also spreads ates a much 
more rapid rate in the dying bark after a tree is cut. 
Vitality of mycelium— The mycelium does not seem to be injured in 
the least by freezing. It remains alive in all parts of the canker during 
the winter. Cultures were kept frozen for a month at a time, and resumed 
growth naturally on being brought back into the laboratory. The 
mycelium is not readily killed by desiccation. Bark removed from 
a canker and kept perfectly dry in the laboratory for ten months yielded 
quite as successful isolations as did fresh bark. Chips of diseased bark 
left on the ground in the woods were found to contain living mycelium 
one year later. This remarkable vitality of the mycelium is one of the 
factors that make the disease difficult to control, 
