No. 634] STENO THERM Y AND ZONE-INVASION 387 



country into life-zones in accordance with the indices 

 thus obtained. Merriam also shows that, by plotting 

 the isotherms of 18°, 22°, and 26° C, for the six hottest 

 weeks of the year, divisions are separated from one an- 

 other corresponding in all essential details to those ob- 

 tained by plotting summation lines. This is practically 

 the method I have used in separating climatic zones of 

 the surface waters of the oceans. Livingston and Liv- 

 ingston (1913) have discussed the system of Merriam 

 and proposed a system of efficiency temperature coeffi- 

 cients which are claimed to represent something more of 

 the basic principles . of physiology upon which the final 

 explanations of distribution should be based. A com- 

 parison between isoclimatic lines plotted for the United 

 States on the direct summation basis and isoclimatic lines 

 plotted on the efficiency indices basis shows a strong, but 

 not absolute tendency toward agreement. The Living- 

 stons, however, do not discuss the interpretation of their 

 charts as regards plant distribution in detail. 



Nearly 30 years ago, while attempting to obtain some 

 idea of the temperature relations of the geographical 

 distribution of the Laminariaceae, I noticed a seemingly 

 definite relation to the lines of mean maxima (summer 

 lines or isotheres) of surface temperatures. Some brief 

 remarks on these relations were published in 1893. Far- 

 ther studies seemed to emphasize the relation between 

 the 10, 15, 20, and 25 degree (Centigrade) isotheres or 

 lines of mean monthly maxima and the limits of distribu- 

 tion of various floral groups, and in 1914 I read a paper 

 at the Twenty-fifth Anniversary Celebration of the Mis- 

 souri Botanical Garden (published 1915) as a prelimi* 

 nary communication on the temperature relation of the 

 distribution of the marine algae as expressed in terms of 

 mean monthly maxima and minima (isotheres and iso- 

 crymes). In this paper, I made a tentative division of 

 the surface waters of the oceans, etc., into zones accord- 

 ing to the courses of the 10°, 15°, 20°, and 25° C. iso- 

 theres, and announced that a rough tabulation indicated 

 that the great majority of species are confined to one or 



