5i8 
DONALD REDDICK 
those engaged in the production of flowers and vegetables under glass, 
and from either standpoint is worthy of further attention. 
The idea of supplying bottom heat has been used extensively by 
florists^ for starting cuttings, but not for growing crops. Plant phys- 
iologists do not seem to have studied the problem, judging by the 
absence of literature on the subject, but this experiment with beans 
and some trials with radish (Raphanus sativus), cucumber {Cucumis 
sativus), and tomato {Lycopersicum esculentum) indicate that root 
temperature and foliage temperature are readily separable as condi- 
tions influencing the grow^th of plants. 
With respect to susceptibility due to environmental changes it 
would seem that in the case of temperature as applied in this experi- 
ment the relation between host and parasite cannot be analyzed 
readily. The experiments show that the host is influenced markedly 
by a change in soil temperature so that it is impossible to make a 
direct comparison of various temperature conditions because of the 
slow action of the parasite. If the parasite made a rapid invasion and 
killed the host outright within a few days there would be an oppor- 
tunity to grow all plants under identical conditions until the day of 
inoculation but even then the sudden change of soil temperature might 
have an even more marked effect on the physiological condition of the 
host, perhaps changing its susceptibility in a very pronounced manner. 
In the case of this disease, and of the majority of root diseases, prompt 
death of the host does not follow because some water continues to 
enter even after the roots have been killed and especially because on 
most plants new roots generall}^ push forth above the point of infection. 
In will be necessary to study under controlled conditions the be- 
havior of the uninfected host when subjected to certain changes in 
this one environmental condition, and that of the parasite in the same 
way, in order to determine the true relation of host and parasite. 
This involves the control of all the known conditions affecting the 
growth of plants, including light, a method for doing which has only 
been hinted at^ to date. 
The physiology of the fungus here used has not been the subject of 
investigation as yet, but in some preliminary experiments on the rate 
of growth of the fungus at different temperatures it was found that 
the diameters of the thalli on bean broth agar in petri dishes varied 
^ White, E. A. The principles of floriculture, p. 162-164. New York. 1915. 
^Livingston, B. E. Plant World 20: 11. 1917. 
