Sept. S3,1918 
Stem Lesions Caused by Excessive Heat 
601 
which are subject to whitespot. It is worthy of note that no cases of 
stem girdle have been found in four seasons’ examinations of the Nebraska 
nursery at which whitespot has been so frequent. The heat hypothesis 
nevertheless seems the best explanation of stem-girdle so far offered. 
Tubeuf’s experiments with warm water (18) are of interest in this con¬ 
nection as indicating that moderately high, long-continued temperatures 
do not necessarily kill simply by their drying effect, as has sometimes 
been claimed. 
LESIONS ON UPPER PARTS OF STEMS 
Older 2-needled pines and herbaceous plans as well have been observed 
by the writer to develop typical shrunken, definitely limited whitespot 
lesions on young growth of the upper parts of their stems, usually at 
points where an abnormal bend had made the surface nearly perpen¬ 
dicular to the sun’s rays. Such lesions seldom girdle stems, and are rarely, 
if ever, of economic importance. 
In the case of Finns strobus the unusual amount of attention which 
pathologists have given it in the last two years has resulted in the finding 
by blister-rust scouts at five different places of yellowish lesions on young 
stems, sunken, and in all or nearly all cases limited to one side of the 
stem. Sections made by Dr. R. H. Colley, of the Bureau of Plant 
Industry, showed a collapsed condition of the tissues, but with absence 
of mycelium. Observations on these lesions in northern Wisconsin by 
Mr. R. G. Pierce, of the Bureau of Plant Industry, showed that prac¬ 
tically all occur on the upper sides of bent shoots or on the west sides 
of vertical shoots, though a single case was found on the north side. The 
greater number of the affected plants were on the west sides of the 
nursery beds. 
Most of these lesions are presumed to be due to heat. In the few cases 
in which soft young shoots of Pinus banksiana have been found girdled 
and bent over at the point of the lesion, mechanical bending is also sug¬ 
gested as a possible cause. 
LESIONS DUE TO EXCESSIVE BENDING 
Following cold weather with high winds, pine seedlings 1 to 2 weeks old 
have been found with white constricted basal lesions in some ways not 
like those produced by heat. There is reason to believe that these are due 
to the constant bending in high wind, at length causing the collapse of 
the cortical tissues without the stress being sufficient at any one time to- 
rupture the epidermis or break the fibrovascular bundles. This is ap¬ 
parently an analogous case to the death of tissue between the veins of 
sugar maple leaves exposed to storm (6, p. 27-28). A few cases of lesions 
on shoots of older pines have already been mentioned as possibly the 
results of mechanical bending rather than of heat, and it is entirely 
possible that the whitespot lesions observed on cowpea seedlings should 
70395°—18-3 
