le 
VEGETABLE 
by differences in the thermal nature of the season 
for one and the same place, and by the difference 
of climate in different latitudes. The wheat- 
harvest begins in the neighbourhood of Naples 
in June, in Central Germany in July, in the 
south of England and in the middle districts of 
Sweden on the 4th of August ; and the barley-har- 
vest takes place at Naples in June, in Central 
|| Germany about the end of July or beginning 
of August, in England on the 14th of August, 
and in the middle districts of Sweden on the 
|| 4th of August. Owing to the comparatively 
higher temperature which prevails in summer 
in Sweden, and to the more rapid vegetation 
there than in England, the wheat-harvest does 
not take place sooner in the south of Hngland 
that at Upsala, but occurs about the same time ; 
and barley is 10 days later of ripening in Eng- 
land than in Sweden. For July, in England, 
has a mean temperature of 60°8° Fahr., and 
about 62°6° Fahr. at Upsala; and August in Eng- 
land has a mean temperature likewise of about 
60°8° Fahr., and in Sweden about the same, 
namely 60°26° Fahr. If we adopt the observa- 
tions made during two years in Saxony, we find 
as the mean result that, from efflorescence to 
ripeness of fruit, 56 days are required for wheat, 
|| 59 for rye, 31 for barley, 45 for oats, and 68 for 
the potato. According to the observations made 
in Wiirtemberg, which were continued for seve- 
ral years, the same period of vegetation required 
56:4 days for rye, 425 for Triticum spelta, 514 
|| for winter barley, 25 for summer barley, and 254 
for oats.—Mere solar heat, however, never ope- 
rates alone on vegetation, but always in accom- 
paniment with heat generated by chemical action 
in the plant and in the soil, and with light, 
electricity, moisture, and the numerous agents 
which are brought into play in the course of vital 
energy and of chemical recombination; and 
therefore the phenomena of variable seasons and 
variable climates are very far from being in uni- 
form accordance with those of variable atmo- 
spheric temperature. The commencing and most 
precarious stage of vegetation, from the germi- 
nation of the seed to the full expansion of the 
foliage, is, for the most part, at least in such 
climates as ours, gone through in comparative 
lowness and unsteadiness of atmospheric heat; 
and the completing and least derangeable stage, 
from the formation of the fruit to the falling of 
the leaf, is gone through in comparatively high 
and steady temperature of both the atmosphere 
and the soil. And instead of vegetating seasons 
of different character capriciously following one 
another in the same manner as the atmospheric 
ones, an early immediately following a late and 
this again immediately following an early, as 
they would do if they were controlled by mere 
temperature, a series or succession of early ones 
is generally followed by a series or succession of 
late ones. Mr. Gorrie remarks that the vege- 
The ripening of the fruit also is controlled both 
| 
PHYSIOLOGY. 067 
tating season about Edinburgh commences about 
the 20th of March, and ends about the 20th of 
October,—that there 40° is the lowest tempera- 
ture at which corn will vegetate, and 56° the 
mean temperature of a good vegetating season,— 
but that in the Carse of Gowrie, nearly half a 
degree further north, a good vegetating season 
seldom occurs, though vegetation there is as for- 
ward as in the vicinity of Edinburgh; and this, 
he adds, is a proof that the progress of vegetation 
is not dependent solely on temperature. He 
notes too, as general results, that the wettest 
seasons are the coldest, and that if very dry sea- 
sons are warmer and earlier, vegetation is less 
vigorous, in consequence of a deficiency of mois- 
ture at the roots.—The ways in which heat ope- 
rates are at once numerous, complex, and recon- 
dite ; and comprise action throughout the plant 
in connexion with vital energy, action within 
the organisms in connexion with electricity and | 
chemistry, action upon the leaves and the epi- 
dermis in connexion with light and atmospheric 
agents, and action within the soil in connexion 
both with the chemical resolution and recombi- 
nation of the principles of nutrition, and with 
the vito-chemical functions of the several parts 
of the seed and the roots. We have not space to 
attempt illustrations of these intricate actions; 
and shall simply refer, in the words of a periodi- 
cal writer, to a small department of one of them 
as an instructive instance of the whole. “Solar 
heat,” remarks this writer, “liquefies and refines 
the vegetable juices; in proportion to that heat, 
therefore, will be their ascent. Heat also ren- 
ders liquids capable of holding a larger quantity 
of salts in solution. These salts form the val- 
uable constituents of vegetables, and are, as it 
were, their frame-work. We have here an ex- 
planation of the rapidity of vegetation in warm 
weather, and also of the fact that warm seasons 
mature the finest grain ; because in these seasons 
the ascending sap will hold the greatest amount 
of salt in solution. The most durable vegetable 
fibre is generally the product of warm climes; 
and we have the fact explained upon these prin- 
ciples, because in these climes it will be composed 
of the greatest amount of least soluble salts.” 
A remarkable law of vegetation, of great con- 
sequence to be well known and understood by 
cultivators, is the counteractive force of luxuri- 
ant growth upon early maturation. In the ani- 
mal kingdom, the chief influences which accele- 
rate growth at the same time accelerate repro- 
duction, so that the period of puberty is uniformly 
earlier in domesticated than in wild animals, and 
in those which are fed plentifully with food, than 
in those which are scantily supplied; but in the 
vegetable kingdom, the reverse of this arrange- 
ment, to a very considerable extent at least, 
prevails. Where plants are furnished with an 
abundant supply of food, their reproductive 
energies are slowly developed, and flowers and 
fruits are late in appearing; and when the sup-— 
