RELATION OF CLIMATE TO SPREAD. 33 
fruits. The probable impossibility of ultimate extermination lias since 
been accepted by Professor Smith and others, who have been most 
interested in this scale and most familiar with it, and best able to judge 
the possibilities in this direction. 
Careful experimentation with remedies, conducted by the division, 
however, has shown the complete feasibility of destroying the scale on 
infested trees. It is, therefore, simply a matter of careful work, accom- 
panied, it is true, with some little expense, to put an orchard in fairly 
good condition: and even if complete extermination is not gained, the 
repetition of such treatment every i'aw years will maintain a condition 
of vigor and fruitfulness which will probably warrant the outlay. The 
slowness with which the insect spreads when limited to its own efforts 
or to natural carriers, such as birds and insects, makes it highly 
desirable for all persons to use the greatest precautions to prevent its 
introduction into their orchards. It emphasizes, also, the importance 
of taking prompt and strenuous measures to stamp it out the moment 
it is found. If we may not, therefore, look forward to eliminating the 
San Jose scale from the list of Eastern fruit pests, we may at least hope 
to check its further spread and effect its extermination in every case 
where it has been recently introduced. 
RELATION OF CLIVCATE TO SPREAD. 
The very extensive studies of the distribution of animal life in this 
country, and incidentally of plant life, conducted by Dr. 0. Hart Mer- 
riam, have defined with approximate accuracy a number of well-marked 
climatic districts or life zones within which particular animals or plants 
thrive and outside of which the}' fail to establish themselves. The 
life zones thus limited have a special value in indicating the possible 
spread of many injurious insects, and we have suggested that they 
may prove to be particularly significant in the case of the San Jose 
scale. These life zones are: The tropical, occupying small areas in Flor- 
ida 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 and northward. These zones 
will be better understood by reference to the accompanying ma]) | fig. 1 . 
on which also the known distribution of the San Jose scale has been 
plotted. ' 
In the instance of the San Jose scale, it is at least suggestive of 
important possibilities, that although affected nursery stock has for six 
or seven years back been sent to all the fruit-growing regions o\' the 
Eastern States, according to our present information the scale has 
established itself only in regions contained within or near the so called 
austral life zones. Mapping the points of establishment, it is very inter 
'A few infested Localities, referred to in the text, discovered subsequently to the 
preparation of the ma]) are not indicated, 
8090— No. :i 3 
