190 



SCIENCE 



[N. S. Vol. LII. No. 1339 



and fruits abundantly in summer and below 

 the isotliere of 10° C, extends south to the 

 northeastern coast of New Jersey where it 

 develops and fruits at the winter and spring 

 temperature of 5° C, but is sterile and evi- 

 dently quiescent at the summer temperature 

 of 22° C. Since it is a perennial species, it 

 is to be found in the southern portions of 

 its range among the summer subtropical spe- 

 cies of the Long Island Region and this is 

 extremely misleading until the conditions of 

 its existence south are understood. When 

 these are made clear, it stands out as a con- 

 spicuous and convincing example of the nar- 

 row interval of temperature making for per- 

 sistence. 



Connected with these narrow intervals 

 seeming to control persistence in certain 

 groups of species of marine algse and limit 

 their distribution, there is associated the ob- 

 served fact that the 10°, 15°, 20°, and 25° 0. 

 isotherms of the surface waters sharply mark 

 off the life-zones from one another. This 

 conclusion comes as a result of the critical 

 study of the relations of these isotherms to 

 certain well-known division points, or de- 

 marcation areas, between distinct floras. In 

 a recent study of the relation of Cape Cod 

 to the florag of the New England coast, where 

 I had at hand detailed information of greater 

 abundance, variety and accuracy than it is 

 generally possible to obtain about such mat- 

 ters, I found that the isothere of 20° C. 

 certainly seemed to divide very sharply the 

 northern species as to their distribution, from 

 the southern. The details of this investiga- 

 tion will be published elsewhere, as it is un- 

 necessary to go into them here, but I desire 

 to mention one which will emphasize the 

 point I am trying to make evident. At the 

 entrance to Vineyard Sound, between Gay 

 Head on Martha's Vineyard and Sow and Pigs 

 off the southern end of the Elizabeth Islands, 

 as Sumner and Davis (1913) have shown in 

 various charts, the surface temperatures in 

 sunmaer are slightly above and the bottom 

 temperatures are slightly below 20° C. and 

 the southern species are found in the surface 

 waters, while the northern species inhabit the 



depths. This, it must be remembered, is only 

 one example of a considerable number which 

 might be cited, to show how abruptly species 

 stop or start in their distribution at one or 

 another of these isotherms. The marine algse 

 extend slightly below 0° C. Thus far I have 

 not been able to determine satisfactorily the 

 conditions at the 5° C. isothere, but the S° 

 isocryme seems possibly a limiting line. 

 There can be no question, as it seems to me, 

 but that the isotherms, both isotheres and 

 isocrymes, of 10°, 15°, 20°, and 25° C. defi- 

 nitely limit the extension of particular floras 

 of marine algse and that too, very sharply and 

 exactly. 



The explanation of the narrovsaiess of the 

 temperature interval seemingly, at least, of 

 such paramount influence in controlling dis- 

 tribution, is by no means clear. If we lay 

 stress on the interval of 5° C. which seems 

 to control reproduction, we have no physio- 

 logical basis at present apparent. If we con- 

 sider the probability that the normal interval 

 of each zone and its peculiar flora, is 10° C, 

 then we may perhaps feel inclined to suggest 

 that each marine algse may persist up to the 

 point where its initial vital activities, in 

 accordance with the working of the van't 

 Hoff-Arrhenius principle, may be doubled in 

 velocity, but no more. In case this may be 

 the proper explanation, the interval of 10° C. 

 seems to be more exact and regular than it 

 has been found to be even as determined for 

 purely chemical reactions. Possibly the tem- 

 perature intervals may have to do with the 

 varying viscosities of the sea-water or its 

 power to dissolve gases such as oxygen or 

 carbon dioxide. On the other hand, it may 

 have to do with the activities of some par- 

 ticular enzyme or group of enzymes which act 

 effectively, as these are known to do, only 

 within narrow limits of temperature. I feel, 

 therefore, that I can do little more at the 

 present time, than to lay emphasis on the nar- 

 rowness of the interval and the seeming im- 

 portance of the maximum and minimum iso- 

 therms very closely approximating 5° C. apart. 

 William Albert Setchell 



Uniyiesitt or Calitoenia 



