Jan. 17,1916 
Plenodomus fuscomaculans 
761 
It is commonly admitted that the description of an organism must be 
taken under the assumption of some definite environment. The great 
mass of media in common use, the uncertainty of composition, the lack 
of standardization, and the usual failure to bring about fructification 
have left the description of fungi with only the natural habitat as a fixed 
environment. With forms of comparatively simple morphology this 
standard has led to the classification by hosts, with its attendant multi¬ 
plicity of species. A firm basis for taxonomy can be arrived at, and 
simplification can come, only from a standardized environment. 
As has been indicated in the preceding discussion, the physical environ¬ 
ment must also be defined. With the growth of our knowledge of the 
forms we shall be able to a great extent to analyze the complex of forces. 
In the present paper one such force has been emphasized and its action 
discovered to be related to the liberation of energy by oxidation. 
Light was found to be essential for reproduction. If light be absent 
or insufficient, although all other requirements were satisfied—with a 
medium suitable for growth and food supply, aeration, acid reaction, 
temperature, all within the proper limits—pycnidium production will 
not take place. Instead, aerial mycelium is formed, and eventually the 
organism goes into a static condition. The light factor, as others, has its 
limits. Weak light will not allow pycnidium production. This factor 
differs from the others in that its action need not be continuous. It is 
therefore of direct stimulative nature. A short exposure to strong 
diffuse light of cultures from dark conditions, which are otherwise ready 
for pycnidia formation, gives the necessary stimulus during a further 
period in the dark. When the effect of the stimulation is spent in the 
production of a few pycnidia, a second exposure is necessary for a second 
inauguration of the process. 
The action of light in thus unlocking these forces is very satisfactorily 
explained by the experiment in which a few drops of hydrogen peroxid 
were used to replace the light stimulus. Other oxidizing agents also 
serve to stimulate fruit-body formation. The protoplasm of well-nour¬ 
ished mycelium is rich in oily reserve materials, and the action of light 
may oxidize these bodies and change them from emulsions of poor mobil¬ 
ity to materials of great diffusibility. Accompanying this we have a 
releasing of energy, and fruit-body formation is inaugurated. The 
mechanism of this process is not known at all, but Herzog (1903) has 
shown that the sporulation of yeast is affected by temperature, and the 
curve for the variation in amount produced by temperature is a typical 
enzym curve. 
Hydrogen peroxid added to a pea-broth culture, to a rich sugar solu¬ 
tion, or to a young growing culture on corn broth does not immediately 
lead to fruit-body formation, nor does the action of light on such cultures 
lead to it. The action of light is modified and controlled by the condi- 
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