238 The 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, 

 Dioscorea 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 



