602 
Journal of Agricultural Research 
VoL XIV. No. X3 
be attributed to bending rather than to heat. Basal stem-girdle lesions 
found on 4-months-old wild olive seedlings (Elaeagnus sp.) and charac¬ 
terized by very slight vertical extension may be due to excessive bending. 
However, stem lesions caused by bending without breakage are not 
believed to be common enough to give rise to serious confusion with 
those caused by heat. 
PREVENTIVE MEASURES 
Assuming the correctness of the hypothesis that most of them are 
caused by heat, the logical procedure for preventing whitespot and the 
basal lesions on older stems is to avoid soils especially liable to overheat^ 
ing, and in established nurseries where trouble occurs, to artificially 
prevent heating. Soil with loose texture or dark surface is presumed 
most likely to overheat at the surface. Shading and frequent light 
watering have already been found helpful in preventing whitespot. 
Encouraging free air movement and artificially compacting the soil to 
increase its conducting capacity have been suggested as having prophy¬ 
lactic value. 
SUMMARY 
(1) Very young seedlings of conifers and certain other plants were 
found dying in large numbers in a Nebraska nursery from a disease 
which, because of its characteristic lesions, the writer has called “white- 
spot.” The trouble has been found, though less commonly, in other 
localities. It is distinct from the common damping-off disease, but 
resembles it so closely that it is very likely to be confused with it. The 
lesions do not seriously interfere with the upward movement of water. 
(2) The location of the whitespot lesions on the stems, their observed 
relation to insolation and to dry surface soil, and the production of typical 
lesions by artificial heating, indicate excessive heat as the cause of most 
of the whitespot trouble. 
(3) The observation in the surface soil in the seed beds in question, 
and by other investigators in other places, of temperatures well over 50° 
C., with reported maxima as high as 68°, further substantiates the 
hypothesis that whitespot is due to excessive heat. 
(4) Killing lesions on stems of older conifers ranging in age from 
several months to 4 years, are also attributed to heat. The causal 
importance of heat in these lesions on woody or semiwoody stems is less 
well established than in the case of whitespot. Further experimental 
work at temperatures such as actually occur in nature is necessary to 
settle finally the pathological importance of high soil temperature. 
(5) Lesions involving young cortex and resembling those attributed 
to heat are probably in some cases caused by repeated bending in heavy 
wind without visible breakage. These are believed to be too rare to 
give rise to serious confusion. 
