VARIETIES IN PLANTS. 
which their vapours assume. The vapour of 
water is lighter than air, at the same tempera- 
ture and under the same pressure, in the propor- 
tion of 1,000 to 1,604; but the vapour of alcohol 
is half as heavy again as air, and that of ether is 
more than twice and a half as heavy. See the 
article Gas. The determination of the height of 
the plane of watery vapour in the atmosphere, is 
a desideratum of great meteorological import- 
ance, and connects itself with all the most in- 
teresting questions regarding the distribution of 
aeriform water over the globe, and regarding the 
irrigation of the continents. But one of the 
best and most recent attempts toward it, made 
in a series of experiments during Sir James 
Ross’s voyage of discovery to the Southern Seas, 
was in a great measure a failure, and attained 
no more than a vague approximation, “giving 
an elevation of about 2,000 feet as its mean 
height in the tropical regions.” See the article 
ATMOSPHERE. 
VARIETIES IN PLANTS. The tendency is 
more or less common in all plants, to vary from 
the character first stamped upon them. ‘This 
disposition is increased by removal from their 
native climate or locality, and greatly by culti- 
vation. By a constant selection of some parti- 
cular quality in successive crops, a gradual re- 
moval from the character of the original is ef- 
fected. Most of our finest fruits, we have reason 
to believe, have been gradually produced by the 
improvement of the original native kinds. The 
improvements effected in former ages, were 
doubtless the result of accident, as the ancients 
were ignorant of the means for their systematic 
accomplishment, The greatest progress in the 
art which has been made in modern times, was 
effected by Van Mons in Belgium, and by Knight 
in England. 
The former, who directed his labours chiefly 
to the pear, produced many new and excellent 
varieties, by a constant and successive selection 
of the best seedlings. He first made a large col- 
lection of natural stocks, choosing those which, 
from the appearance of the wood and leaf, he 
had reason to believe, would be most likely to 
produce the best fruit. As soon as the first of 
these bore, he selected the best, and planted the 
seeds. Selections were again made from the 
first fruit of these, and so on in continued suc- 
cession, the best and soonest in bearing were 
uniformly chosen. He thus obtained fruit from 
the eighth generation; each successive experi- 
ment yielding an improved result on the preced- 
ing. At the fourth generation many of the 
fruits were good, several excellent, but a smaller 
number still bad. He had, in the early part of 
this series of experiments, no less than eighty 
thousand trees ; hence in selecting from so large 
a number, his chance for fine ones was vastly 
greater than from a small collection ; and hence 
too the reason why, after seven or eight improv- 
ing generations, he had obtained so many hun- 
Sess 
eee 
VASCOA. 557 
dred fine sorts. In the early stages of his opera- 
tions, he found “that twelve or fifteen years 
was the mean term of time, from the moment of 
planting the first seed of an ancient variety of 
the domestic pear, to the first fructification of 
the trees which sprung from them. The trees 
from the second sowing, yielded their first fruit 
at an age of from ten to twelve years; those of 
the third generation, at an age of from eight 
to ten years; those of the fourth generation, at 
an age of from six to eight; and those of the 
fifth generation at the age of six years. Van 
Mons, being actually at the eighth generation, 
has informed me,” says Poiteau, “that he has 
obtained several pear trees which fruited at the 
age of four years.” When his seedlings were at 
the age of three or four years, he was able to 
judge of their appearances, though they had not 
as yet borne; such only were taken for further 
trial, as exhibited the strongest probability of 
excellence. It is hardly necessary to remark 
that in all these trials, the young trees were 
kept in the highest state of cultivation. Van 
Mons maintained that, by planting the seeds of 
the first crop, the product would be less liable to 
run back to the original variety, than where the 
seeds were taken from a crop produced on an 
old bearing tree; and to this practice he chiefly 
ascribed his success. 
The production of new varieties is greatly fa- 
cilitated by cross-impregnation, or by intermix- 
ing the pollen and stigma of two varieties, for 
the purpose of procuring something of an inter- 
mediate nature. This was performed with great 
success by Knight. Selecting two varieties for 
operation, while yet early in flower, and before 
the anthers had burst and discharged the pollen, 
he cut out with a:fine pair of scissors all the 
stamens, leaving the stigma untouched. When 
the stigma became mature, he introduced the 
pollen (the fine dust of the bursting anthers) of 
the other variety, either by shaking the flower 
of the latter, deprived of its petals, over the 
stigma, or by transferring it on the point of a 
camel’s-hair pencil, from one flower to the other. 
The seeds of the fruit, thus yielded, partake of 
the nature of both; and the trees growing from 
them, bear fruit of various intermediate mix- 
tures.—Thomas’s Fruit-Culturist.—See the article 
Hysripizine or Puants. 
VARRONIA. A genus of ornamental, exotic, 
ligneous plants, of the cordia family. About 
a dozen species, all white-flowered evergreens, 
varying in natural height from 4 to 30 feet, have 
been introduced to British collections, princi- 
pally from tropical America; and about 20 more 
are known. All the introduced species are pro- 
pagable from cuttings; most love a soil of sandy 
loam ; and one, the alder-leaved, ranks in its na- 
tive country as a fruit-tree. 
VASCOA. A small genus of ornamental, Cape- 
of-Good-Hope, yellow-flowered, evergreen shrubs, 
of the genista division of the leguminous order. 
