VENTILATION. 
they interpose screens of oiled paper between 
the earth and the air of their houses; and in 
their pits for vegetables they cover the surface 
of the ground with the same oiled paper, by 
which means vapour is effectually intercepted, 
and the air preserved from excessive moisture. 
“Tn forcing-houses, ventilation is thought to 
be required at the time when the fruit is ripen- 
ing, for the purpose of increasing the perspira- 
tion of the plants, and, consequently, of assisting 
in the elaboration of the secretions to which 
fruit owes its flavour. But, even for this, its 
utility is, perhaps, overrated,—and it is quite 
certain that it may be easily carried to excess; 
for, if it is so powerful as to injure the leaves by 
over-drying the air, an effect the reverse of what 
was intended will be produced; that is to say, 
the quality of the fruit will be deteriorated. 
Upon this subject Mr. Knight has made the fol- 
lowing observations:—‘A less humid atmo- 
sphere is more advantageous to fruits of all kinds, 
when the period of their maturity approaches, 
than in the earlier stages of their growth; and 
such an increase of ventilation, at this period, as 
will give the requisite degree of dryness to the 
air within the house, is highly beneficial, pro- 
vided it be not increased to such an extent as to 
reduce the temperature of the house much below 
the degree in which the fruit had previously 
grown, and thus retard its progress to maturity. 
The good effect of opening a peach-house, by 
taking off the lights ef its roof during the period 
of the last swelling of the fruit, appears to have 
led many gardeners to overrate greatly the bene- 
ficial influence of a free current of air upon 
ripening fruits; for I have never found ventila- 
tion to give the proper flavour or colour to a 
peach, unless that fruit was, at the same time, 
exposed to the sun without the intervention of 
glass; and the most excellent peaches I have 
ever been able to raise were obtained under cir- 
cumstances where change of air was as much as 
possible prevented, consistently with the admis- 
sion of light (without glass) to a single tree.’ 
“ Tt is not improbable that one of the advan- 
tages of ventilation depends upon a cause but 
little adverted to, but which certainly requires 
to be well considered. It was an opinion of Mr. 
Knight, that the motion given to plants by 
wind is beneficial to them by enabling their 
fluids to circulate more freely than they other- 
wise would do; and in a paper printed in the 
Philosophical Transactions for 1803, he adduces, 
in support of his opinion, many experiments and 
observations; of which the following is suffi- 
ciently striking :—‘ The effect of motion on the 
circulation of the sap, and the consequent for- 
mation of wood, I was best able to ascertain by 
the following expedient. arly in the spring of 
1801, I selected a number of young seedling 
apple trees, whose stems were about an inch in 
diameter, and whose height between the roots 
and first branches was between 6 and 7 feet. 
VENUS'S NAVELWORT. 
These trees stood about 8 feet from each other; 
and, of course, a free passage for the wind to act 
on each tree was afforded. By means of stakes 
and bandages of hay, not so tightly bound as to 
impede the progress of any fluid within the trees, 
I nearly deprived the roots and lower parts of 
the stems of several trees of all motion, to the 
height of three feet from the ground, leaving 
the upper part of the stems and branches in 
their natural state. In the succeeding summer, 
much new wood accumulated in the parts which 
were kept in motion by the wind; but the lower 
parts of the stems and roots increased very little 
in size. Removing the bandages from one of 
these trees in the following winter, I fixed a 
stake in the ground, about 10 feet distant from 
the tree, on the east side of it; and I attached 
the tree to the stake at the height of 6 feet, by 
means of a slender pole, about 12 feet long ; thus 
leaving the tree at liberty to move towards the 
north and south, or, more properly, in the seg- 
ment of a circie, of which the pole formed a ra- 
dius; but in no other direction. Thus circum- 
stanced, the diameter of the tree from north to 
south in that part of its stem which was most 
exercised by the wind exceeded that in the op- 
posite direction, in the following autumn, in the 
proportion of thirteen to eleven.’ Now, if the 
effect of motion is to increase the quantity of 
wood in a plant, it is evident that ventilation, 
which causes motion, must tend to produce a 
healthy action in the plants exposed to it; and 
such a state must also be favourable to the de- 
velopment of all those secretions upon which the 
organization of flowers, the setting of fruit, and 
the elaboration of colour, odour, flavour, &c., so 
much depend. Some suggestions by Mr. Knight, 
as to the manner in which this result can be 
artificially produced, will be found in the Hort. 
Trans., vol. iv. p.2 and 3; but the subject has 
as yet attracted little attention.” 
VENUS’S COMB. See Saupnerp’s NEEDLE. 
VENUS’S FLY-TRAP. See Muscreuna. 
VENUS’S HAIR. See Marpennair. 
VENUS’S LOOKING-GLASS, See Prismato- 
cARPUS and BELLFLOWER. 
VENUS’S NAVELWORT,—botanically Om- 
phalodes. A genus of ornamental, hardy, herba- 
ceous plants of the borage family. The name 
alludes to the navel-like form of the seeds.—The 
evergreen species, Omphalodes sempervirens, call- 
ed by Linnzeus Anchusa sempervirens, grows wild 
on rubbishy spots of ground in Britain. Its 
root is perennial; its foliage is evergreen; its 
stem is about 30 inches high; and its flowers 
have a blue colour, and bloom from May till 
July. ‘Two evergreen perennial species, and four 
annual species, some with white flowers, others 
with blue flowers, all very handsome and more 
or less nearly allied to the hound’s-tongues, have 
been introduced to Britain from the southern 
parts of Continental Europe; and all thrive well 
on any common soil. 
wn ee 
