302 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 2 



surface of the submerged plant is exposed to one and the 

 same temperature. The problem, therefore, of temperature 

 as a physiological factor in controlling the distribution of 

 algae, in general, and of marine algae in particular, is, as com- 

 pared with that of land plants or of land animals, compara- 

 tively simple. 



Any attempt to unravel the physiological basis for the con- 

 trol of distribution must be, at this point of the progress of 

 the work, lacking sufficient data for conviction. The state- 

 ments presented merely represent approximate optimal con- 

 ditions for the duration, succession, and, therefore, continued 

 persistence of the species of the various life zones. It seems 

 certain that the coefficients for continued existence vary 

 among the different species, but are restricted in the case of 

 each species to about 10° C. in amplitude. There must be for 

 each species a certain minimum and a maximum of optimal 

 temperature for continued life and reproduction. It is pos- 

 sible that certain species may continue to exist outside these, 

 especially if they possess powers of vegetative reproduction. 



Thus far, it has been in mind to attempt to determine co- 

 efficients of efficiency as Livingston and Johnson have sug- 

 gested in the case of climatic factors controlling the distribu- 

 tion of land plants, but no real beginning has, as yet, been 

 made. The interval of 10 °C. certainly suggests the working 

 of the van't Hoff-Arrhenius principle as applied to vital 

 phenomena. Taking the variation of 10° C. as the control- 

 ling interval of temperature and regarding it as an index to 

 the summation of temperature, it may be possible in a later 

 paper to definitely estimate the coefficients of temperature- 

 efficiency in a fashion similar to that already suggested by 

 Livingston and Johnson ('13) for land plants. 



If the rate of the vital activities are, in general, doubled 

 or nearly so with each increase of 10°C, then, judging from 

 the results of the Rhodophyceae, thus far tabulated, it would 

 seem that marine algae cannot endure an acceleration greater 

 than 2, that each species has its own definite initial tempera- 

 ture for efficient vegetative and reproductive activity and that 

 such initial efficient activity may be accelerated up to the 



