296 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



rvoL. 2 



winter isotherms or isocrymes, or any of those in the inter- 

 mediate seasons. 



For example the isothere of 20° C. passes somewhat south 

 of Cape Cod to the eastern end of Long Island, but the shal- 

 low and more or less protected waters of Long Island Sound, 

 Narragansett Bay, Buzzard's Bay and Vineyard Sound carry 

 a higher temperature eastward even to the Cape Cod region. 

 At exposed points, however, the somewhat colder waters of 

 the ocean outside exist and exercise their influence at exposed 

 points or in deeper waters. 



Again at Cadiz, the isothere of 20° C. abruptly curves up 

 to the coast. At Cape Inuboi, Japan, the isothere of 25°C. 

 touches land and at the Strait of Sangar, that of 20° C. The 

 Cape Region of South Africa is included between the isotheres 

 of 20° C. and 25 °C. Similar relations hold good on the 

 coast of Ireland, for the 15°C. isothere comes in just north 

 of Clare Island at about Annagh Head. On the south coast 

 of Australia, the isothere of 20 °C. touches the east coast 

 just above Cape Howe and the south coast about Cape Arid, 

 thus leaving the southeastern coast below 20°C. of average 

 summer temperature and the southwestern coast above it. 

 Although the western coast of North America has its tem- 

 perature relations very much disturbed, as I shall indicate 

 later, yet there is a fairly definite relationship to the isotheres 

 of 10°C, 15°C, 20°C, and 25°C. The arctic or boreal 

 floristic region has a definite southern boundary in the 10 °C. 

 isothere and the subarctic in that of 15°C, while those of 

 the North Atlantic are bounded to the south by that of 25 °C. 

 The strictly tropical species are found almost entirely between 

 the isotheres of 25°C. and 30°C. (or 32°C). It is expected 

 that a later paper will deal more definitely and in more detail 

 with the reasons for selecting the isotheres as boundin 

 for the temperature zones. 



e> 



Two seeming disturbances of those zonal areas may be 



noted 



( Upper 



and Upper Austral) are for 10°C. interval rather than 5°C. 

 This is in accordance with what is known of the distribution 

 of the marine flora in the higher Arctic and the higher Ant- 



