CA cae 
13 
importation their natural enemies, which had preserved a balance between them and 
the vegetable world, are all left behind, and they are free to increase and multiply 
without hindrance or molestation until native parasites and predaceous insects and 
animals acquire the habit of preying upon them. 
Mr. Scudder, in an admirable excursus, speaking of this continent 
only, explains these phenomena by that intensity which seems to 
characterize all life in America, and which, in so far as the human 
race-is concerned, marks us as a restless, hurrying, energetic, enter- 
prising people. In explanation of this condition Mr. Scudder cites the 
greater extremes with us in variation of temperature. The mean annual 
temperature, for example, of New York City and Frankfort is approxi- 
mately identical, but the summer temperature of New York is that of 
Rome, and the winter of St. Petersburg. Changes are also quicker 
from summer to winter, and our Summers are longer and have a marked 
preponderance of sunshine compared with the same seasons in Europe. 
This, according to Scudder, explains the greater virility and fecundity 
seen, especially in the case of animals, on this continent. In illustra- 
tion of this he shows that, as a rule, among all butterflies properly 
comparable on the two continents, that is, as to climatic situations as 
well as generic relationships, there is no single instance where the 
European butterfly has more broods than the American, and very 
generally the latter has one to several broods more than the former. 
As accounting for the comparative freedom of HKuropean agriculture 
~ and horticulture from destructive attacks of insects, the argument from 
the standpoint of climate appeals to me strongly, and has already been 
urged by me in an address before the Entomological Society of Wash- 
ington last year. A personal examination of the conditions_convinced 
me that an unfavorable climate has much to do with the immunity from 
notable damage in Europe as compared with America. The shorter 
and cooler summers of middle Kurope, comparable to our fall and early 
winter almost, do not foster the multiplication of insects as do our 
longer and hotter summers; and furthermore, in Florida and in the 
coast region of California the effect of the longer summers is accen- 
tuated by another favorable condition, viz, the greater humidity as 
compared with the portions of Europe where the crops are similar, as, 
for example, Italy and Spain. 
A purely theoretical explanation noted, but rightly, in my judgment, 
not indorsed, by Dr. Howard in an annual address before Section F, 
American Association for the Advancement of Science, in 1897, is that 
the flora and fauna of America, the older continent, have become degen- 
erate through age and can not successfully resist competition with the 
more vigorous forms introduced from the younger continent of Europe. 
All these explanations, except the first, call for continuous action, 
and the more important of the conditions involved in them doubtless 
exert such influence on all life in the New World, but the phenomena 
with which we are specially concerned, namely, the extraordinary 
