392 



THE AMEBIC AX NATURALIST 



[Vol. LIV 



maximum temperature from 0° C. or below to about 22° 

 C. and seasonal ranges of about 17° C. maximum. Asco- 

 phyllum nodosum is also a perennial species. RJwdo- 

 chorton Rothii is a delicate red alga which, nevertheless, 

 seems to be a perennial andMonostronui Grevillei a mem- 

 branous green alga, and Polysiphonia urceolata, a fila- 

 mentous red alga, are annuals, but with the same range 

 as Ascophyllum nodosum. Grinnellia americana is the 

 last example of many eurythermal alg£e of the Atlantic 

 coast of North America I desire to bring forward. It is 

 a strikingly beautiful annual membranous red alga and 

 extends from northern New England (North Temperate 

 Zone, 15°-20° C, mean max.) to the coast of North Caro- 

 lina (Tropical Zone, 25 80 C, mean max.). Other ex- 

 amples of eurythermal species might be given, but those 

 I have mentioned are typical and reasonably well known. 

 They will serve as a good representative basis for dis- 

 cussion with the idea in mind that what is indicated by 

 the eurythermy of one and another of them will, by an- 

 alogy, also seem extremely possible to be the case with 

 all other types and individual species extending over 

 ranges of temperature of more than 10° C. 



Stenothermal species are particularly characteristic 

 of the Tropical Zone, in very few portions of which the 

 seasonal variation in temperature is over 10° C. Species 

 confined to the Upper Boreal or to the Upper Austral 

 Zones are also narrowly stenothermal, since the entire 

 range of temperature in these zones is not over 10° C. 

 The temperate and subtropical zones are usually suffi- 

 ciently affected by seasonal changes to show a range 

 of temperature greater than 10° C, but in the southern 

 hemisphere in particular, there are portions of these 

 zones, at least, that show only a 10° C. range and conse- 

 quently may possess stenothermal species. The annual 



