No. 034] STENOTHERMY AND ZONE-INVASION 397 



Zone (20°-25° C). North of Cape Cod, it is to be found 

 only in certain warm protected spots where the insola- 

 tion is sufficient to raise the temperature to that of the 

 subtropical zone- while the* waters outside are those of 

 the temperate zones. To the south of the North Sub- 

 tropical Zone the species is a winter annual and follows 

 the 20° C. isocryme. Grinnelia is, therefore, a steno- 

 thermal and not a typical eurythermal species and in- 

 vades both colder and warmer zones, the colder because 

 of warm spots and the warmer because of favorable sea- 

 sonal conditions. 



Farlow, in his Marine Algae of New England, has am- 

 ply explained still a different type of invasion, viz., from 

 a colder zone into a warmer and I have some additional 

 details in a paper soon to be published. The Laminari- 

 acecr, or kelps, a number of species of perennial red 

 algae, some other browns, greens, reds, etc., pass Cape 

 Cod and are to be found in the colder waters which are 

 usually the deeper waters to the south of it. This seems 

 to be an invasion from the North Temperate into the 

 North Subtropical. It does not mean, however, as is 

 the case also with the examples I have mentioned and 

 discussed, that these seeming invaders are living in 

 waters of a different range of temperature from that of 

 the normal zone. Their eurythermy is but seeming, at 

 least so far as this particular invasion is concerned. 



In conclusion, I may say simply this: stenothermy is 

 the rule both from the point of view of distribution and 

 of physiology, at least so far as effective reproduction is 

 concerned; eurythermy is largely, if not entirely, a 

 matter of endurance of a wide range of temperature, 

 much of which endurance is due to the power to enter 

 into a condition of rigor after certain extremes of tem- 

 perature of either direction are passed; and a study of 

 the various reasons for zone invasion assists greatly in 

 making these facts apparent. 



