764 
Journal of Agricultural Research voi. v. No. 16 
range of cases. Their teachings can not, however, be made the basis for 
research without the development of methods of attack suitable to a 
series of forms. The method of this paper may be used for similar 
organisms. 
The first part of the paper may be interpreted as a determination of 
the limits of the life processes, which, when once determined, allow in 
the latter part of the paper a manipulation of them. The knowledge of 
the factors and their optima made possible a development of an environ¬ 
ment especially fitted for growth and reproduction. 
The proposition of Klebs, that the limits of reproduction are narrower 
than those of growth, is fully substantiated. Klebs further pointed out 
that growth and reproduction are processes opposed to each other. This 
is true for the organism studied. 
The action of light has led to an insight into the mechanism of this 
opposed action. It has shown that growth, the static condition, is 
opposed to reproduction, a dynamic condition. Where one process is 
storing energy, the other is a process consuming energy. The equilib¬ 
rium within the cells needs to be upset by some oxidizing force in the 
case of this fungus to inaugurate fruit-body formation in susceptible 
mycelium. 
It is not concluded from the experiments with this species that light 
is a specific factor which will cause reproduction to take place in all 
forms, once growth is checked, although it may be expected to be an 
important condition in related organisms. But, in view of the great, 
similarity of behavior in all the forms tested so far with respect to growth 
and reproduction, it may be concluded that in them some stimulus be¬ 
comes operative when an organism is in the hunger state which starts the 
utilization by oxidation of the stored food supply and leads to the phe¬ 
nomenon of reproduction. 
SUMMARY 
This paper gives the results of experiments performed with Plenodomus 
fuscomaculans , a fungus pathogenic to the apple. The specific problem 
undertaken was the determination of the effects of various controlled 
environmental factors upon the growth and reproduction of this fungus. 
The historical development of the art of culturing organisms has been 
traced from the first crude cultures to the present elaborate technic. 
The simultaneous development of our knowledge of the physiology of 
organisms has been briefly summarized. This survey shows that the 
environmental factors may greatly influence the life processes of organ¬ 
isms. Organisms have been cultured in the laboratory in an imitative 
or haphazard way, with a chance of finding a suitable environment. 
Owing to the great variety of available methods and the great plasticity 
of organisms, this course has been productive of results with some forms. 
Another type of research has sought to find the relation of the organism 
