566 
ways in which the root crops are beneficial to 
his land,—that they are means in his hands for 
altering the texture of the soil,—that they afford 
him opportunity of cleansing and well stirring 
it, &c. This is very true; but after all, it will 
be found that their most important function is, 
as before said, the collection and preparation of 
food for the cereals. The root crops may be cal- 
led the nurses of the tender and helpless corn 
plants; like nurses, they themselves require 
food, but their organs are of a nature to render 
them less dependent upon the character of that 
food. Food is, indeed, the first consideration to 
plants as well as animals. Give a man plenty of 
wholesome nutritious food, and he will be com- 
paratively safe from the attacks of disease, and 
indifferent to the inclemency of the weather. 
Stint him in the supplies of this first necessary, 
and you leave him an easy prey to both. Is it 
otherwise with plants? Surely not—they too 
must be fed; if nature does not supply them 
liberally enough, the care of man must make 
good the deficiency; but until he knows what 
they require, his efforts can hardly fail of being 
in many cases abortive, or, where successful, 
attended with unnecessary waste. And here we 
come to the point from which we started; the 
cereals require two kinds of manuring, mineral 
and vegetable—the roots require principally on- 
ly one, the first of these. Supply your roots with 
mineral nourishment, and whilst by the increase 
of their produce you are enabled (so to speak) to 
grow a larger quantity of mutton and beef and 
milk, you will ensure also a more abundant re- 
turn of the more valuable crops, for which the 
turnip and mangold wurzel eventually become 
the mineral as well as vegetable sustenance.” 
The connexion of heat with vegetable life and 
growth is intimate and manifest, yet involves 
questions of much intricacy, and is so inter- 
woven with accompanying connexion of light, 
electricity, moisture, and chemical reaction as 
to present many and strong obstacles to search- 
ing investigation. A power is evidently possessed 
by the living plant of preventing the freezing of its 
sap amid a temperature far below that at which 
the inmost juices of the same plant when dead 
would become frozen; but what that power con- 
sists in, or through what precise means it ope- 
rates, further than the theoretic certainty of its 
essential connexion in some way or other with 
life, is utterly unknown. Plants, indeed, in some 
ways or through some organ or in some particu- 
lar stages or functions of their growth, are ca- 
pable of generating very considerable quantities 
quantity to be perceptible, and may be supposed 
to form it by the inhalation of oxygen and the 
burning of carbon in a particular organ or 
organs in some such method as is done by ani- 
mals in the organs of respiration; and though 
the texture of such organ or organs is so exceed- 
ingly minute as to have hitherto eluded actual 
VEGETABLE PHYSIOLOGY. 
observation, their existence may be satisfacte- 
rily inferred, not only from the general fact of 
generated heat being evolved, but from the par- 
ticular one that oxygen is inhaled by petals as 
distinctively as carbonic acid is inhaled by leaves, 
and especially is absorbed in large quantity by 
flowers at the instant of fecundation—Yet the 
temperature which mainly affects plants is not 
that which originates within themselves, but 
that which is suffused around them in the soil 
and in the atmosphere. A certain degree of 
exterior temperature is necessary to every plant 
for the germination of its seeds, the development 
of its flowers, and the maturation of its fruits; 
and as this very largely depends upon climate, 
it both controls the native adaptation of differ- 
ent species of plants to different zones and alti- 
tudes of the world, and powerfully modifies the 
phenomena of vegetation in any one species 
when removed from its native region to one 
which is either considerably colder or consider- 
ably hotter. The seeds of tropical plants, when 
sown in temperate climates, germinate much 
later than in their native regions,—and when 
sown in gardens, require such a considerable 
elevation of temperature as can be obtained only 
in greenhouses or on hotbeds or in stoves; and 
those of cold countries bordering on the frigid 
zones, When sown in temperate climates, germi- 
nate much earlier than in their native regions, 
—and when sown in gardens, require to be de- 
posited in the coldest and most shady spots of 
the open ground. A difference of temperature, 
in any one district, in one and the same season 
in different years, likewise exercises a great 
influence on the epochs of germination, so that, 
not unfrequently, the seeds of the same plants 
germinate much earlier when the spring arrives 
soon, and a mild rainy winter had preceded it, 
but much later when the heat of spring has been 
delayed by a severe winter. The unfolding of 
the leaf buds, and the development of the flow- 
ers are also subject to the same changes which 
are observable in the germination of seeds. Ac- 
cording to observations made, at the request of 
Schiibler, by the naturalists assembled at Berlin 
in the autumn of 1828, during the following 
summer at Parma in Lombardy, and in various 
places farther to the north, the same plants 
flower at Zurich 6 days later than at Parma, 
at Tubingen 13 days later, at Jena 17, at Berlin 
25, at Hamburgh 33, at Greifswald 36, and at 
Christiana no less than 52 days later than at 
Parma. In higher latitudes, in districts situ- 
ated in the north of Germany, the development 
of vegetation is less retarded than in more south- 
ern positions; for the delay of the development 
of efflorescence between Hamburgh and Chris- 
tiana amounts to only 3:4 days for one degree’s 
approach towards the north, while that between 
Southern Germany and Smyrna, which is in the 
same parallel as the most southern portions of 
Europe, amounts for the same space to 7’4 days. 
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of heat, and sometimes evolve it in sufficient 
