240 
Journal of Agricultural Research 
Vol. XXIV. No. 3 
Any theory which could be postulated to explain the pathological 
disturbances in seemingly healthy individuals would naturally contain 
much of the hypothetical and be antecedent to our present knowledge 
of physiological phenomena. Temporary and local changes in the 
metabolism may cause the production of substances toxic to young and 
delicate cells. Microorganisms, which have occasionally been isolated 
from normal plants, could, under certain conditions, cause physiological 
disturbances with accompanying cytological changes. Mechanical in¬ 
juries may directly or indirectly produce similar effects. However, in 
the latter case it should be possible to trace the origin of the diseased 
area and to determine whether the cause was external or internal, and 
this has often been accomplished. 
INFLUENCE OF ENVIRONMENT 
An insight into the effect of environmental factors on the anatomical 
structure was obtained by studying a number of potato varieties grown 
at the high altitude station at Fort Lewis in Colorado. By taking ad- 
