METEOROLOGY. 
19 
elusions with respect to the climate of ancient Europe and 
Asia, are those drawn from the accounts given by the classical 
writers of the growth of cultivated plants; but these are by 
no means free from uncertainty, because we can seldom be 
sure of an identity of species, almost never of an identity of 
race or variety, between vegetables known to the agriculturists 
of Greece and Rome and those of modern times which are 
thought most nearly to resemble them. Besides this, there is 
always room for doubt whether the habits of plants long 
grown in different countries may not have been so changed 
by domestication that the conditions of temperature and 
humidity which they required twenty centuries ago were 
different from those at present demanded for their advan¬ 
tageous cultivation.* 
* Probably no cultivated vegetable affords so good an opportunity of 
studying the laws of acclimation of plants as maize or Indian corn. 
Maize is grown from the tropics to at least lat. 47° in Northeastern 
America, and farther north in Europe. Every two or three degrees of 
latitude brings you to a new variety, with new climatic adaptations, and 
the capacity of the plant to accommodate itself to new conditions of tem¬ 
perature and season seems almost unlimited. We may easily suppose a 
variety of this grain, which had become acclimated in still higher latitudes, 
to have been lost, and in such case the failure to raise a crop from seed 
brought from some distance to the south would not prove that the climate 
had become colder. 
Many persons now living remember that, when the common tomato 
was first introduced into Northern New England, it often failed to ripen; 
but, in the course of a very few years, it completely adapted itself to the 
climate, and now not only matures both its fruit and its seeds with as 
much certainty as any cultivated vegetable, but regularly propagates itself 
by self-sown seed. Meteorological observations, however, do not show 
any amelioration of the summer climate in those States within that 
period. 
Maize and the tomato, if not new to human use, have not been long 
known to civilization, and were, very probably, reclaimed and domesti¬ 
cated at a much more recent period than the plants which form the great 
staples of agricultural husbandry in Europe and Asia. Is the great power 
of accomodation to climate possessed by them due to this circumstance ? 
There is some reason to suppose that the character of maize has been sen¬ 
sibly changed by cultivation in South America; for, according to Poppig, 
