552 Seed-Breeding. [August, 
of generations, that these will become established as per- 
manent. 
The produ(5tion of variations in a plant is easily acccom- 
plished. Any interference with the normal condition will 
cause them — a change of climate ; a little more or less heat 
or moisture ; the influence of crossing with the pollen of 
another variety ; or an interference with the growth of the 
plant; or abundant or scant nutrition: all these, of the 
more evident causes, are effe(5tual. A small eared, 8-rowed 
Canada corn, removed to a more genial clime than where it 
has been grown, increases in height of plant and in length 
of ear ; a little greater change, and the tendency to increase 
of rows of grain on the cob becomes manifest. An 8-rowed 
flint-corn, removed and cultivated in Ohio, in one instance, 
became, from seven years’ use, closely allied to gourd seed, 
being much dented, and the number of rows on the cob had 
increased to twelve and twenty. In Louisiana, the conti- 
nued cultivation of soft gourd seed-corn from the West 
produced a hard flint-corn with a larger cob, in twelve 
years. This change, which is too well recognised to require 
further illustration, is also accompanied by a change in the 
habit of growth of the plant, which is not confined to the 
shape, and structure, and composition of the seed, but also 
to the habits of maturity, — the seed from northern localities, 
the first year after removal, ripening earlier than the vari- 
eties native to the region, but shortly approximating the 
periods common to the locality. It is this fa<5t which 
enables the extension of culture into localities whose tem- 
perature will not admit of the immediate transference from 
southern sources, but which can be entered through the 
gradual cultivation through intermediate stations. Thus 
the potatoes, which require five months for their develop- 
ment in Germany, are cultivated, according to Leopold von 
Buch, in Lyngen, two degrees beyond the polar circle, and 
attaining their full development in little less than three 
months. The feature to be noted in these cases is, that 
these variations, brought about through means at the con- 
trol of man, become fixed in the variety. 
The effects of temperature and moisture are of great avail 
towards changing the habits of the plant, yet from the 
nature of the case cannot be well separated and defined. 
We have observed a difference in the transpiration of water 
from different plants, a variation which is of extreme im- 
portance as leading to the selection of that variety which 
requires the least water for the processes of growth, for 
planting in drouthy localities, and vice versa . Heat alone, 
