238 T/ie Philippine Journal of Science 1916 
While the growth farther from the apex, which would have 
produced nutation and twining, ceased in most plants in darkness, 
the length of growing region and the activity of zones somewhat 
remote from the apex did not change uniformly. If this region 
was especially active, nutation was possible very much as in light. 
In a number of stems in darkness, always especially vigorous 
specimens, there was an unmistakable movement, apparently in 
the distinctive form of normal nutation; and in a single case, 
Dioscore a aculeata No. 88, dark soil No. 3, the main stem being 
broken and replaced by a very vigorous branch, the latter, during 
the three days preceding May 16, wound three times around a 
stick of wood in a perfectly regular spiral. 
Growth is a complicated process. Defined as a change in form 
or size, it of course includes metabolic processes that find no 
expression in the definition. Environmental conditions that find 
an expression in growth may do so in a variety of ways, which 
have hitherto escaped adequate analysis. Aside from metabolism 
taking place in the region or structure that actually grows, the 
growth of higher plants is dependent in all cases upon changes 
taking place elsewhere in the plants. In the case of the yams, 
the growth of the distal part of the growing shoot depends upon 
the metabolic processes taking place in the food store, by which 
the food is made available for removal, and upon the transloca- 
tion of this food from the place of storage to the place of use. 
It has already been indicated that the rate of growth varies 
with the temperature. Aside from the effect of temperature 
exerted directly on the growing region, which effect may itself 
be subject to analysis, temperature may have an influence upon 
the preparation of the food for translocation or on the rate of 
translocation itself. For the analysis of the problem into three 
phases — metabolic processes in the food store, translocation, and 
processes in the growing region itself — Dioscorea is an especially 
suitable subject for study. The experiments that I have made 
along this line are no more than introductory. However, the 
question is an important one, and the methods are believed to be 
worthy of general use. For these reasons, the tentative and 
inclusive experiments already made are reported here. 
The investigation of the influence of temperature on the pro- 
cesses taking place in the food store was made by the very simple 
and obvious device of inserting a part of the tubers in ice water, 
and comparing the growth of the corresponding shoots with that 
of the shoots of plants, the whole of which were kept under 
ordinary laboratory conditions. The results of this experiment 
are recorded in Table VIII, showing the growth of plants of 
