240 Influence of Environment on Plants 
help of any available hypothesis for points of attack, which may enable 
us to acquire a more complete mastery of physiological methods. 
To quote a single example; I may put the question, what internal 
changes produce a transition from vegetative growth to sexual repro- 
duction ? 
The facts, which are as clearly established for the lower as for the 
higher plants, teach us that quantitative alteration in the environ- 
ment produces such a transition. This suggests the conclusion that 
quantitative internal changes in the cells, and with them disturbances 
in the degree of concentration, are induced, through which the 
chemical reactions are led in the direction of sexual reproduction. 
An increase in the production of organic substances in the presence 
of light, chiefly of the carbohydrates, with a simultaneous decrease 
in the amount of inorganic salts and water, are the cause of the 
disturbance and at the same time of the alteration in the direction 
of development. Possibly indeed mineral salts as such are not in 
question, but only in the form of other organic combinations, par- 
ticularly proteid material, so that we are concerned with an alteration 
in the relation of the carbohydrates and proteids. The difficulties 
of such researches are very great because the methods are not yet 
sufficiently exact to demonstrate the frequently small quantitative 
differences in chemical composition. Questions relating to the 
enzymes, which are of the greatest importance in all these life- 
processes, are especially complicated. In any case it is the necessary 
result of such an hypothesis that we must employ chemical methods 
of investigation in dealing with problems connected with the phy- 
siology of form. 
Il. INFLUENCE OF ENVIRONMENT ON THE TRANSFORMATION 
OF SPECIES. 
The study of the physiology of form-development in a pure species 
has already yielded results and makes slow but sure progress. The 
physiology of the possibility of the transformation of one species into 
another is based, as yet, rather on pious hope than on accomplished 
fact. From the first it appeared to be hopeless to investigate physio- 
logically the origin of Linnean species and at the same time that of 
the natural system, an aim which Darwin had before him in his 
enduring work. The historical sequence of events, of which an 
organism is the expression, can only be treated hypothetically with 
the help of facts supplied by comparative morphology, the history 
of development, geographical distribution, and palaeontology’. A 
glance at the controversy which is going on to-day in regard to 
different hypotheses shows that the same material may lead different 
1 See Lotsy, Vorlesungen (Jena, 1. 1906, 11. 1908), for summary of the facts. 
