44 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9 
Having indicated some of the general benefits likely to accrue from the 
application to physiology of that clause in the physicist's creed that ex- 
presses belief in the quantitative relationships existing among the various 
characteristics and attributes of a material system, we may turn to an ex- 
ample of this clause as a means, perhaps, of making the idea more concrete. 
1 refer to a principle proposed by Le Chatelier^ and by Braun,^ and often 
termed Le Chatelier's theorem. This principle states that all systems are 
conservative, or, in extenso, "Each change in an outer condition that affects 
a body or a system produces in it a change in such a direction that as a re- 
sult of this change the resistance of the body or system to this outer change 
is increased." ° This law, so far as physics and chemistry are concerned, 
is perfectly general, indeed it is embodied in the second law of thermo- 
dynamics, and there is thus additional reason for believing it to be operative 
in biology.^ 
Biologists long since adopted as a fundamental principle of their science 
what seems to be the same law stated in biological terms: they said that 
organisms tend to adapt themselves to changes in their environment. If 
an outer condition afTecting the plant is altered, the plant alters within 
itself in such a way as to adjust its activities to the new state of affairs and 
to maintain recognizably its individuality. 
It must now be noted that the Le Chatelier-Braun theorem implies 
always a connection between the directions of two processes that may occur 
in the body or system. If one of the processes is known, the theorem 
indicates the necessary existence and the direction of action of a second 
process.^ It is with this connection that we are concerned today rather 
than with the theorem itself : that there is an interrelationship of plant proc- 
esses which should be statable mathematically. This corollary should be 
as nearly universally true as the theorem itself. 
It should be further noted that the ''outer condition" of the theorem 
need not be outside the plant, for, since energy transformations occur in- 
side the plant, portions of the plant may be "bodies or systems" in the 
sense of the theorem and be affected by changes in other conditions within 
the plant; the theorem is concerned with the energy relations of processes 
and their determining conditions, which are, in turn, expressions of other 
processes, and not with their spatial arrangements. Thus the introduction 
of a coil of wire between the poles of a magnet calls forth energy readjust- 
^ Le Chatelier, H. Sur un enonce general des lois des equilibres chimiques. Compt, 
Rend. Acad. Sci. Paris 99: 786-789. 1884. 
^ Braun, F. Untersuchungen iiber die Loslichkeit fester Korper und die den Vorgang 
der Lqsung begleitenden Volum- und Energieanderungen. Zeitschr. Physikal. Chem. i: 
259-272. 1887. 
^ Chwolson, O. D. Lehrbuch der Physik 3: 475. Ubersetzt E. Berg. Braunschweig, 
1905. 
^ For discussions of this theorem from biological standpoints see Hooker, H. D., Jr. 
Behavior and assimilation. Amer. Nat. 53: 506-514. 1919, and the literature there cited. 
7 Chwolson, O. D. Loc. cit. 475, 476. 
