Vermont farmer. [volume] (Newport, Orleans County, Vt.) 1870-1877, 1875-04-23
Principles of Horticulture.
XI. AIR AND LIGHT.

277. When an embryo plant is formed
within its integuments, it is usually color
less, or nearly so but, as soon as it begins
to grow, that part which approaches the light
1.-THE steml becomes colored, while the oppo-
site extremity 1.-THE root) remains colorless.
27S. The parts exposed to the air ab-
sorb oxygen at night, absorb carbonic acid
and part with oxygen again in daylight and
thus in the daytime purity the air and render
it fit for the respiration of man.
279. The intensity of this latter phe-
nomenon is in proportion to the intensity Of
solar light to which leaves are directly ex-
posed.
$50. Its cause is the decomposition Of
carbonic acid, the extraction of oxygen aud
the acquisition by the plant of carbon in a
solid state; from which, modified by the
peculiar vital actions Of species, color and
secretions are supposed to result.
28l. For it is found that the intensity of
color, and the quantity of secretions, are in
proportion to the exposure to light and air,
us is shown by the deeper color Of the upper
sides of the leaves, etc.
2S2 And by the fact that, if plants be
grown in air from which light is excluded,
neither color nor secretions are formed, as
is exempli6ed in blanched vegetables which,
If even naturally poisonous, may, from want
Of exposure to light, become wholesome, as
celery.
2S3. When any color appears in parts
developed in the dark, it is generally caused
by the absorption of such cooring matter as
pre-exlsted in the root or other body fro IN
which the blanched shoot proceeds, as in
some kinds Of rhubarb when forced
2S4. Or by the deposition Of coloring
matter formed by parts developed in light,
as in the subterranean roots of beets, car
rots, etc.
285. What is true Of color is also true
of flavor, which equally depends upon light
for its existence; because flavor is produced
by chemical alterations in the sap ca used by
exposure to light.
2S6. The same thing occurs in regard
to nutritive matter, which in like manner is
formed by exposure OF leaves to light.
Thus the potato, when forced in dark
houses, contains no more amylaceous matter
than previously existed in tho original tuber,
but acquires it in abundance when placed 10
the light, and deposits it in proportion as it
is influenced by light and air. Thus, also,
if peaches are grown in wooden houses, at a
distance from the light, they will form SO
little nutrtive matter as to be unable to
support crop of fruit, the greater part Of
which will fall off. And for a similar
reason, it is only the outside shoots of stan
dard fruit trees that bear fruit. Considera-
tions OF this kind form in part the basis of
pruning and training.
287. Light is the most powerful stimu-
lus that can be employed to excite the vital
actions of plants, and its energy is in pro-
portion to its intensity; 80 that the direct
rays Of the sun will produce much more
powerful effects than the diffused light of
day.
2SS. Hence, if buds that are very excit-
able are placed in diffused light, their
eIcitability will be checked.
2S9. And ii buds that are very torpid
are exposed to direct light, they will be
stimulated into action.
29O. So that what parts Of the tree
shall first begin to grow in the spring may
be determined at the will OF the cultivator.
29l. This is the key to some important
practices in forcing.
292. This should also cause attention to
be paid to shading buds from the direct rays
of the sun in particular cases as in that oi
cuttings, whose buds, if too rapidly excited
might exhaust their only reservoir of sap,
the stem, before new roots were formed to re.
pair such loss.
293. As plants derive an essential part
of their food from the air by the action Of
light, it follows that in glass houses those
which admit the greatest portion of light are
the best adapted for purposes of cultiva'
tion.
294. The proportion Of opaque matter
in the roof of glass house constructed Of
wood varies from one-thrd to one-seventh
that Of an iron house does not exceed one
twenty third.
295. Therefore, iron-roofed houses are
in this respect better suited for cultivation
than wooden.roofed houses.
296. And it has been found by expert
Inent that light passes more freely through &
curvlinear than through a plane roof, and
through glass forming an acute angle with
the horizon than through perpendicular
glass it follows that a curvilinear roof il
best, andA plane roof with glass perpen
dicular sides the worst, adapted to the pur'
poses OF the cultivator.
297. For the same reason common greer
glass is less fited for glazing forcing houses
than white crown glass.
298, Poisonous gases in very minut,
quantities act upon vegetation with grea
energy. A ten'thOusandth part of sui phur
Gus acid gas is quickly fatal to the life o
plants; and hence the danger of Aues heat
ed by coal fires, aud the impossibility o
making many species grow in the vicinity o
houses heated by cOalfres or in large towns