1922] Setchell,—Cape Cod and the Marine Flora 5 
work covers the coast from Buzzards Bay to the shoal waters off and 
above Chatham, Massachusetts. This region is a mixture of enclosed 
shallow waters, exposed points, and intruding deeper waters and the 
flora is, in consequence, a mixture of northern and southern species. 
The data given and the charts of the detailed distribution of the 
individual species are sufficiently numerous to indicate very exactly 
the difference in the distribution of the two types of species. In the 
report of Davis, on the marine algae of the district, we have the definite 
proof of the statements of Farlow and of Collins. 
My own collecting along the coast of New England has been more or 
less extensive and in 1893, I made a reference to Cape Cod as a divid- 
ing line in the kelp-flora of the eastern coast of North America. I 
also made the statement (1893, p. 370) that the isothere, or line of 
mean maximum temperature of the surface waters of the north 
Atlantic Ocean, for 20° C., touched the shore in its neighborhood. The 
paper of 1893, although dealing only with the Laminariaceae or kelps 
so far as distribution is concerned, has opened up the larger question 
of climatic distribution in general for all organisms and paved the way 
for the papers on the geographical distribution of the marine algae 
published in 1915, 1917 and 1920. "Through the data afforded by 
demarcation areas such as that of Cape Cod, but situated on all 
coasts throughout the world, I have divided the photic belts of the 
neritic shelves of the coasts of the world into climatic zones according 
to mean maxima of the surface waters, For reasons which I have 
given elsewhere, it has seemed most natural to establish nine climatic 
or temperature zones extending from the far north to the extremes of 
marine plant life in the south and these, with the exception of the two 
polar zones may be considered to be limited by surface isotheres 5? C. 
apart. The coast of New England is divided between the North Tem- 
perate Zone, between the isotheres of 15? C. and 20° C. and the North 
Subtropical Zone, between the isotheres of 20? C. and 25? C. The 
question, therefore, of the relation of the 20° C. isotheres to Cape Cod 
is vital to any discussion of the climatic zones as I have attempted 
define and delimit them. 
In checking over and tabulating the species of marine algae of New 
England so kindly and generously provided by Mr. Collins, I find 
that there are 551 species, varieties, and forms at present to be 
accredited with some considerable certainty to the coast. Of course, 
there is some uncertainty in a few cases, but apparently less so than 
