1] UPON THE RATE OF GROWTH 455 



This table shows, first, that the optimum, minimum, and 

 maximum are correlated ; that when one is high or low the 

 others are, in general, high or low also. It shows, moreover* 

 that the position of the optimum varies greatly ; so that the 

 minimum of one species, Bacillus thermophilus, lies higher 

 than the maximum of another, Bacillus phosphorescens. We 

 see, also, that the bacteria have, among all organisms, the great- 

 est variation in the optimum, for this ranges from 20 to 63- 

 70 C., or through 43-50 C. In the various phanerogams the 

 extreme range of the optimum is from 26.6 to 33. 7 C., or 

 through 7. Again, the range of temperatures at which 

 growth occurs in any one species varies greatly. The most 

 striking feature of this table the one which most needs 

 accounting for is its variety. 



In respect to the optimum we find a certain relation between 

 the degree of temperature of most rapid growth and that to 

 which the organism is normally subjected. Taking the case of 

 an organism with a low optimum, we find Bacillus phosphores- 

 cens living in the North Sea, and normally subjected to a low 

 temperature ; for, even in its southern part, the mean temper- 

 ature of the North Sea is 17.5 at the surface. Taking the 

 case of organisms with a high optimum, we find Bacillus an- 

 thracis and Bacillus tuberculosis living in the mammalian body 

 at a normal temperature of 35 to 38 C. These numbers lie near 

 the optima of the species. Bacillus thermophilus lives in fer- 

 menting manure and in other situations attaining a temper- 

 ature of 60 to 70. Likewise, among phanerogams, we find a 

 relation between the optimum and the normal temperature 

 the maize and gourd are of tropical origin, while the white 

 mustard (Sinapis) belongs to the temperate zone. That this 

 agreement between optimum and normal temperature is not 

 always close may be partly ascribed to the fact that many spe- 

 cies of plants, especially cultivated plants which are usually 

 employed in experimentation, have lived at different times 

 under dissimilar environmental conditions. What, now, is the 

 reason for this general parallelism between the optimum and 

 the normal temperature ? As in other cases, it can clearly be 

 ascribed only to an attunement gained by the organism as a 

 result of its subjection to the temperature. 



