MODIFICATION OF VEGETATIVE AND REPRODUCTIVE FUNCTIONS 413 
that carbohydrates and nitrogenous nutrients are the only compounds con- 
cerned in the varying expression of vegetative and reproductive functions. 
The results of recent experiments on the application of sulphur to certain 
leguminous crops, as well as those from the use of potash, phosphorus, and 
many other substances, would refute any such idea; they were considered 
in detail simply because there are available a large number of ponderable 
analyses concerning them and because they have long been favorite material 
for speculation. 
To determine the role of water in respect to the varied plant functions 
is in itself a large problem. Not only must its direct effects in so far as it 
enters into chemical combination be deciphered, but a knowledge of its 
physical influences and of its direct consequences in the rendering available 
or non-available of other materials is also imperative. The effects of light 
and temperature, both on vegetation and on reproduction, will undoubtedly 
eventually find their clearest interpretation when studies have been made 
relative to the influence of these agencies on internal composition, and to 
how they are related to observed changes. How either light or temperature 
reacts upon the type and rate of water and salt absorption, upon the relative 
proportions of salts absorbed, and upon the processes of photosynthesis, 
metabolism, and storage, remains in large part still to be exactly determined. 
Then, too, what limits to the range of expression of any character, or func- 
tion, or groups of characters or functions, are imposed by hereditary factors 
on the one hand, or by physiological factors on the other — if actually there 
is a possibility of separating them — remains for the geneticists, cytologists, 
and physiologists to determine. 
From the physiological and morphological viewpoint, the several con- 
tributions by Klebs at once come to mind as being the most outstanding, 
both because of the range of forms investigated and of the number of 
environmental conditions considered. It is to be regretted that his work 
has not contributed a larger mass of data concerning the actual internal' 
conditions and composition of the plants investigated. For the most part 
he has examined external conditions and external responses, and from the 
data thus obtained reasoned as to what might be the most probable internal! 
situations and effective elements in producing the observed results. 
Several other workers, however, have published analyses of plant tissues, 
such as the apple, the olive, and other species, on the basis of which it is 
possible definitely to correlate in a quantitative way the vegetative or 
reproductive tendencies of such forms with certain elements of their com- 
position. There are also scores of recorded analyses of various plants which 
show the wide variations in composition of any particular species or variety 
at various stages of its development or maturity. It is unfortunate that 
many of these results are fragmentary and do not form a part of a series 
sufficiently long to admit of determining the range of effects of specific 
substances under a varied set of conditions. Nor are they sufficiently 
