720 
Journal of Agricultural Research 
Vol. V, No. 16 
; But the organism, when inoculated into the host, gave characteristic 
lesions and typical pycnidia from which the organism could again be 
isolated. These reisolations were repeatedly tested, with results parallel 
to those obtained from the parent culture. Certain fungi—e. g., Botryo- 
sphaeria ribis and Rhizoctonia spp.—are known to fruit exclusively upon 
the host, and evidence seemed to point to this organism as one of that 
type. 
EXPERIMENTS UNDER CONTROLLED CONDITIONS 
In 1913, experiments were begun at the University of Michigan labora¬ 
tory. In this work an attempt was made to find the effects of varying 
environmental factors, or, in other words, to analyze the formative as 
well as the inhibiting factors involved in growth and reproduction. 
CONDITIONS FOR GROWTH AND REPRODUCTION 
Physical Factors 
light 
The influence of light upon organisms has been recognized for a long 
time. Fries (1821) and the early authors attributed great morphogenic 
power to light. They found their greatest substantiation of the effect of 
light upon organisms in the excessive growth of mycelium in caves, 
accompanied, as it was, by the suppression of fructification. The litera¬ 
ture is full of these observations, many of which are quoted by Elfving 
(1890). Scientific experiment with light as a factor influencing growth 
and reproduction of fungi began with the classic studies of Brefeld (1877, 
1881, 1889) on Coprinus spp. Brefeld found in some species a complete 
suppression of fructification when cultures developed in the dark; in 
other species fructification took place, but the growth was puny. In 
some the high temperature of the summer replaced in part the beneficial 
effect of light. In a set of interesting experiments Brefeld showed that 
the exposure of mycelium to light need not be long (two to three hours) in 
order to have fructification begin, and that cultures so exposed developed 
normally, although in the dark. The work of Brefeld substantiated that 
of the older observers. Takon (1907) has attempted to show that the 
action attributed to light is really due to transpiration differences in the 
cultures of Coprinus spp. 
Downes and Blunt (1878) had previously experimented with the effect 
of light upon bacteria and found that it had a very detrimental effect upon 
these organisms. This they attributed to the action of the ultraviolet 
rays in augmenting oxidation, a property of light long recognized by 
chemists. Their conclusion was later substantiated by Ward (1893). 
Elfving (1890) gave the results of his experiments with light in a mono¬ 
graph on the subject. Searching the literature, the only important 
experimental work found was that of Brefeld (1877, 1881, 1889) already 
