DECEMBER 27, 1918] 
3. Evidence of the long period the disease 
has been present in the trees themselves; 7. e., 
bare, weathered tops; healed cankers; thrifty 
branches, with bases diseased and hypertro- 
phied, but living, ete. 
4. Peculiarities of the bark; such as ex- 
tensive development of a callus tissue, and the 
presence of a peculiar substance which is con- 
stantly associated with, and particularly con- 
spicuous in cases of marked resistance. 
5. The natural grouping of the trees in well- 
defined areas or “pockets,” pointing to a 
genetic variation. 
6. The manifestation by members of the same 
coppice group; and by branches, trunk and 
basal shoots of the same individual; of similar 
degrees of resistance, indicating an inherent 
condition. 
If these facts and inferences are correct, 
they point the way clearly toward a recon- 
struction and a revival of our American chest- 
nut. Many of the trees bloomed well, and 
this fall bore good fruit. A large number of 
nuts have been gathered and planted by Dr. 
Van Fleet, of the U. S. Department of Agri- 
culture, at the trail grounds near Washington, 
D. C. If the resulting seedlings substantiate 
the inference that the disease resistance is a 
heritable character, the way lies open, both by 
inbreeding, and by crossing with the resistant 
oriental species (not good timber trees them- 
selves) to develop an extremely resistant or 
perhaps practically immune strain of timber 
tree for the reforestation of our devastated 
chestnut woodlands. 
ArtTHur HarmMounT GRAVES 
OFFICE OF INVESTIGATIONS IN ForEST PATHOLOGY, 
Bureau or PLANT INDUSTRY, 
WasHINGTON, D. C. 
THE OCCURRENCE OF AZOTOBACTER IN 
CRANBERRY SOILS 
SEVERAL papers have appeared recently in 
Scrence and elsewhere’ * concerning the fact 
that the aerobic non-symbiotic nitrogen fixing 
organisms, namely the Azotobacter group, oc- 
cur in the soil, when the concentration of the 
1Gainey, Scrence, Vol. 48, pp. 139-140, 1918; 
Jour. Agr. Res., Vol. 14, pp. 265-271, 1918. 
2 Gillespie, Science, Vol. 48, pp. 393-394, 1918. 
SCIENCE 
653 
hydrogen-ion is not more than 10°, or the lim- 
iting exponent is 6.0. 
Investigators* have gone so far as to use 
the presence of Azotobacter in the soil as an 
indication of the soil reaction. Gillespie,? in- 
terpreting the results of Christensen,® stated 
that they are in accord with those obtained by 
Gainey, namely the limiting hydrogen-ion ex- 
ponent for the presence of Azotobacter in the 
soil is 6.0. 
The methods previously used in determining 
the soil acidity conveyed only a very indefinite 
idea about the true nature of the reaction of 
the soil. But only recently *5 methods have 
been suggested which, either using the electro- 
metric or an improved colorimetric method, 
have enabled us to get a better insight into 
the extent and nature of soil acidity. These 
studies have brought out the facts referred to 
above concerning the reaction limit for the 
existence of Azotobacter in the soil. 
In the study of the microbial population of 
cranberry soils some interesting observations 
were made and of these only the occurence of 
Azotobacter will be reported here. 
The cranberry soils are so distinctly differ- 
ent from ordinary soils that it was thought 
for a long time that no very large number of 
bacteria can exist in them and that the mi- 
crobial population consists predominantly of 
molds. These soils are known to have a dis- 
tinetly acid reaction and contain large quanti- 
ties of undecomposed organic matter, namely 
the roots and the stubble of the dead plants. 
The existence of Azotobacter in cranberry soils 
would be of great practical importance, since 
the nitrogen of the air would thus be fixed 
and made available to the crops, which have 
to grow in soils rather poor in available nitro- 
genous constituents (particularly is this true 
of sandy bottom bogs). The undecomposed 
roots and stubble would supply the carbohy- 
drates necessary for the activities of Azoto- 
8 Christensen, Soil Science, Vol. 4, pp. 115-178, 
1917. 
4Gillespie, Jour. Wash. Acad. Sci., Vol. 6, pp. 
7-16, 1916. 
5 Sharp and Hoagland, Jour. Agr. Res., Vol. 7, 
pp. 123-145, 1916. 
