Ii8 
NEIL E. STEVENS 
Endothia parasitica and those showing the temperature of the various 
locaHties is remarkable. This together with the evident lack of agree- 
ment between the rate of growth and the amount of rainfall, strongly 
suggests that the rate of growth of this fungus while growing as a 
parasite on Castanea dentata, is influenced chiefly by temperature. 
The data presented in this and the preceding paper indicate clearly 
that the growth of the chestnut-blight fungus is more rapid in the 
southern portion of its present range than in the region farther north. 
Unless some unforeseen factor checks its development, the disease 
may reasonably be expected to spread still more rapidly as it advances 
southward. 
Summary 
The lateral growth of cankers of Endothia parasitica on Castanea 
dentata in various localities was about the same for the year ending in 
May, 1916, as for the year ending in May, 1915. 
Neither amount nor frequency of rainfall seems to have any 
influence on rate of lateral growth. Wide differences in the rainfall 
for the two years produced no change in rate of growth. 
The temperature for the period under investigation was computed 
according to the systems of "remainder summation indices," ''expo- 
nential summation indices," and "physiological indices." Of these 
the last seems to agree least well with the rate of growth of E. parasitica. 
The first two systems give practically identical results. 
The agreement between the curves of temperature and of growth 
is so close as to indicate that temperature is the chief climatic influence 
in determining the rate of growth of Endothia parasitica. 
Investigations in Forest Pathology, 
Bureau of Plant Industry, 
Washington, D. C. 
LITERATURE CITED 
1. Lehenbauer, P. A. Growth of Maize Seedlings in Relation to Temperature. 
Physiol. Res. i: 247-288./. 4. 1914. 
2. Livingston, B. E., and Livingston, Grace J. Temperature Coefificients in Plant 
Geography and Climatology. Bot. Gaz. 56: 349-375,/. 3. 1913. 
3. Livingston, B. E. Physiological Temperature Indices for the Study of Plant 
Growth in Relation to Climatic Conditions. Physiol. Res. i : 399-420. 19 16. 
4. Stevens, Neil E. The Influence of Certain Climatic Factors on the Development 
of Endothia parasitica, Amer, Journ. Bot. 4: 1-32. 1917. 
