CHIEF ENVIRONMENTAL CONDITIONS. 133 



The last-named author studied the influence of temperature upon the 

 rate of growth of barley, and his results seem to show (see Russell's 

 graph, page 21) that the temperature coefficient here varies markedly 

 with the temperature itself. Since later workers have failed to record 

 the same conclusion, it seems that Russell may perhaps give to 

 Bialoblocki's results too conclusive a weight. It is clear that in some 

 cases, at least, the operation of the law of the minimum^ may interfere 

 in such experimentation, thus precluding the full acceleration affect 

 of a given rise in temperature. As Livingston and Livingston (1913) 

 have pointed out, "it seems highly probable that complex vital 

 processes such as growth may frequently fail, under natural condi- 

 tions, to exhibit the chemical temperature coefficient. In some of 

 these cases proper alterations in other environmental factors might 

 disclose the otherwise masked coefficient, in other cases the limita- 

 tions might be internal, as in the nature of the protoplasmic mixture, 

 and the obscuring of the coefficient might persist in spite of any 

 attempt at external adjustment." 



In favor of the supposition that growth-rates of plants do show a 

 temperature coefficient of 2.0 or above, may be mentioned the experi- 

 mental studies of Price," who determined the temperature coefficients 

 for the opening of flower-buds on cut twigs of the plum, peach, apple, 

 and other fruits. The time period required for resting buds to pro- 

 duce flowers was shown to be reduced about one-half for each rise in 

 temperature of 10° C. Lehenbauer's^ extensive study of the relation 

 of growth rate, in shoots of maize seedlings, to maintained tempera- 

 ture shows much more clearly than had ever been done before how 

 important the duration factor is in determining the effect of tempera- 

 ture on growth. As regards the temperature coefficient, he found that 

 this has a value of from 2.40 to 1.88 for a range of temperature from 

 20° to 32° C, the seedlings being exposed to the given temperature 

 for 12 hours. For temperatures below 20° the coefficient has higher 

 values (for the decade from 12° to 22° its value is 6.56) and for tem- 

 peratures above 32° the coefficient is much lower (for the decade from 

 33° to 43° it is 0.06). 



Our present knowledge of this whole matter leads to the idea, as 

 Livingston and Livingston have stated, ''that there are many cases 

 in which growth-rates and other complex processes in plants and 

 animals exhibit temperature coefficients of about 2.0, and that in 

 other cases this same coefficient is probably operative but is obscured 

 by the limiting effect of some other environmental condition." These 

 authors also point out that temperature coefficients of other orders of 

 magnitude than that given may be expected, both for elementary and 



^ Blackman, F. F. (1908), Idem, (1905). — Mitscherlich, E. A., DasGesetz des Minimums und 

 das Gesetz des abnehmenden Bodenertrages, Landw. Jahrb. 38: 537-552, 1909. — Idem, Ueber daa 

 Gesetz des Minimums und die sich aus diesem ergebenden Schlussfolgerungen, Landw. Versuchs- 

 stat, 75: 231-263, 1911. 



^ Price, H. L., The application of meteorological data in the study of physiological constants. 

 Ann. Kept. Virginia Agric. Exp. Sta., 1909-10: 206-212, 1911. 



^ Lehenbauer, 1914. 



