AMERICAN 
JOURNAL OF BOTANY 
Vol. VII December, 1920 No. 10 
THE MODIFICATION OF VEGETATIVE AND REPRODUCTIVE 
FUNCTIONS UNDER SOME VARYING CONDITIONS 
OF METABOLISM! 
E. J. Kraus 
In virtually any text on the subject of plant physiology may be found 
paragraphs dealing more or less definitely or indefinitely with the functions 
of the so-called essential elementis. Many of these treat of the relationships 
which specific elements or compounds have to the modification of repro- 
ductive or of vegetative functions, considering these either as separate 
entities or as mutually interdependent. Large numbers of contributions 
dealing with specific phases of the subject are constantly forthcoming from 
the fields both of research and of practice. Some of these are in the nature 
of deductions made largely on hypothetical grounds while others are based 
upon experiments of varied nature. The field which can be well covered 
by any investigator is limited, though the opportunity for constructive 
work is large. Much must be done in the way of assembling and inter- 
preting the results of various investigations, especially in connection with 
the extended researches in chemistry, physics, and the related sciences on 
the one hand and with the practices of the applied sciences on the other. 
Granting all this, it is self-evident that at this time we can scarcely do 
more than state the problem as it now seems to exist, and take a brief look 
at its possible future development. As time goes on it seems less and less 
possible to express any dogmatic opinions, or to draw any narrowly circum- 
scribed conclusions from the data available. 
Disregarding the notion that any circumstance which threatens the 
life of a plant causes such a plant to become markedly reproductive in 
order that the species may be perpetuated, one of the earliest attempts to 
explain, on a physiological basis, the apparently interrelated phenomena 
of vegetative extension and the differentiation of parts more intimately 
concerned in sexual reproduction, assumed that any of the higher green 
plants is in a state of adjustment between the materials which it derives 
from the soil and those substances which it manufactures from these ma- 
^ Invitation address read before a joint session of the Botanical Society of America, 
the American Society for Horticultural Science, and the American Phytopathological 
Society at St. Louis, December 31, 1919. 
[The Journal for November (7: 355-408) was issued December 7, 1920.] 
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