THE RELATION OF CLIMATE TO SPEEAD. 33 
the actual conditions of infestation are perhaps as well known in this 
State as in any other. In many localities the scale is held in check by 
this careful system of inspection and by the prompt and thoro 
adoption of the remedial treatment. 
CANADA. 
On the authority of Dr. James Fletcher, the Dominion entomolo- 
gist, the San Jose scale infestation in the eastern portion of Canada is 
confined to the Niagara Peninsula and counties along the north shore 
of the west end of Lake Erie. It has also been found in several locali- 
ties in British Columbia, having reached this province in its northward 
migration along the Pacific slope. 
THE RELATION OF CLIMATE TO SPREAD. 
This subject was rather carefully considered in both Bulletins 3 and 
12, in connection with the climatic districts or life zones established 
b} T Dr. C. Hart Merriam, within which particular animals thrive 
and outside of which they fail to establish themselves. These 
life zones as thus limited have a special value in indicating the 
probable spread of many injurious insects, and seem to be par- 
ticularly significant in the case of the San Jose scale. These life zones 
are: The tropical, occupying small areas in Florida and southern Texas; 
the lower and upper austral, covering the bulk of the United States; 
and the transition zone, coming between the last and the boreal zone 
of Canada northward. These zones will be better understood by refer- 
ence to the accompanying map (PI. V). The earl} T records led to the 
belief that the San Jose scale would be practically limited to the upper 
and lower austral zones, and that the important fruit districts in the 
northern United States and in elevated mountain regions, represented 
by the transition zone, would be slightly if any infested. In the main, 
the records of the distribution of the San Jose scale have confirmed 
this belief. Nevertheless, the scale has, in a number of instances, 
appeared well into the transition zone as fixt by Doctor Merriam, 
notably in Massachusetts, in New York, in Michigan, and a few other 
points; but in most of these cases the evidence gained from the rela- 
tion of other animals and plants would indicate that the transition and 
upper austral zones were not correctly charted, so that in general the 
belief in the immunity of the transition zone holds. 
As pointed out by Doctor Howard in Bulletin 12, the coastal law 
which brings about the intermingling of northern and southern forms 
will probably justify the eastern Massachusetts occurrences. Other 
occurrences in Massachusetts are justified by the river-valley law in 
relation to the Connecticut River, and Doctor Merriam admits that his 
line across the • southern peninsula of Michigan is not very accurately 
