§1] 



UPON THE RATE OF GROWTH 



457 



the maximum for B. tuberculosis of man, is likewise about the 

 human ultra-maximum ; and 30°, the minimum for B. tubercu- 

 losis, is just below the human ultra-minimum. Thus the 

 range of vital temperatures of this parasite is practically the 

 same as that of its host. 



To sum up, the critical temperatures of plants are wonder- 

 fully adjusted to their environment, not only in respect to 

 the optimum for growth, but also in respect to the range 

 within which growth is possible. The origin of this adjust- 

 ment is, as the phenomena of acclimatization show, not to be 

 sought in any process of selection, but in the modification 

 wrought on the protoplasm by the temperature itself. 



2. Animals. — We may begin our account of the effect of 

 heat on the rate of growth of animals by a table, necessarily 

 drawn from more limited data, but otherwise resembling 

 Table XLVII. 



TABLE LI 

 Showing foe Diiteeent Tempekatdres the Absolute Increase in Length, 



MEASURED IN MILLIMETERS, FROM THE 24tH TO THE 48tH HoUE AFTER 



Hatching. Measurements made on Young Tadpoles of the Frog, 

 . Eana viresoens, and the Toad, Euro lentiginosus, by Lilue and 

 Knowlton, '98 



Oscar Heetwig ('98) has determined the curves of growth 

 for Rana fusca, and these are given in Fig. 131. These curves 

 have not been carried beyond the optimum. (Compare Fig. 129.) 



This table and the curves show plainly that the growth of 

 organisms so remote as the maize plant and tadpoles are simi- 

 larly affected by heat. In both cases there is a slow and con- 



