124 Hydration and Growth. 



The conception of a temperature coefficient of growth must be taken 

 as an integration of the action of a constellation of forces acting upon 

 colloidal material of varjdng constitution.^ The agencies in question 

 do not run parallel in their effects and interlock in the most intricate 

 manner.^ It is not surprising, therefore, to find that the coefficient of 

 temperature as applied to growth, which is usually calculated in terms 

 of relative effect for each variation of 10° C, has but little usefulness, 

 except between 10° and 30° C.^ The value of Q^° as it is usually written 

 varies between 1.12 and 5 or 6, and the variation in any given organism 

 is usually very great above 30° or 35° C. Thus, in my own experi- 

 ments with Opuntia, the actual range of growth was found to extend 

 from as low as 7° C. under some circumstances to 51.5° C. under others, 

 but no single individual was seen to grow throughout this range. The 

 combination of conditions which would enable it to do so are not likely 

 to occur in a state of nature and would be difficult to bring about 

 experimentally. 



In addition to the complexities of interplay of molecular forces to be 

 reckoned with — and they appear most formidable to the chemist 

 familiar with their nature — the application of ratios or formulae to 

 variations in growth produced by temperature in the higher plants 

 encounters still other difficulties. Chief among these is the fact that 

 the growing region of a plant may vary in actual and relative amounts 

 of embryonic cell-masses and of fixed non-expanding tissues. External 

 measurements of elongation, even when applied to root-tips, may have, 

 in consequence, but doubtful value. 



A brief description has been given on page 96 of the unsatisfied 

 water capacity of the corms of Brodicea, from the apices of which two 

 or three leaves 20 to 30 cm. long arise and elongate by the action of a 

 mass of embryonic cells, which maintain a basal position during the 

 entire development of the leaf. The corms habitually he 5 to 10 cm. 

 below the surface of the soil and the growing region operates under the 

 influence of the soil, not the air, temperature. It was therefore ar- 

 ranged to grow some of these plants in pots, taking the temperatures 

 by thermometers thrust into the soil, in the vicinity of the bulbs. Such 

 cultures in small chambers with thermostatic control yielded some 

 data of interest. An attempt was made to ascertain the relative rates 

 of increase or amount of water which might be absorbed by the corms 

 and by the growing regions of the leaves at different temperatures. 

 A trio of corms, each of which consisted of the older basal corm and 

 the recently formed younger one, having an average height of 12 mm., 

 were at first swelled to saturation at 19° C. and after two days, when 

 quiescence had been reached, the preparation was placed in a warmer 



1 Osterhout, W. J. V. Some aspects of the temperature coefficients of life-processes. Jour. 

 Biol. Chem., 32: No. 1, p. 23. 1917. 



* See Barry, F. The influence of temperatvu-e upon chemical reactions in general. Amer. 

 Jour. Bot., 1: 203-226. 1914. 



