58 
ON CLIMATE. 
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through which the sap ascends, by means of cuttings plunged and kept for a time in purple-coloured 
infusions. During the correspondence with that great man, from the summer of 1830 to within a 
year of his decease, an opportunity occurred to allude to the errors which must inevitably arise from 
any experiments with mutilated members of vegetables ; and, with that frankness which was peculiarly 
his own, he at once admitted that in any case where a plant, or portion of a plant, was so disturbed by 
eradication or mutilation as to interrupt the harmony of vital action that exists between the atmo¬ 
sphere, the plant, its roots, and the earth, by which these are supported, no just or philosophical con¬ 
clusion could be arrived at from experiments under such conditions. The amputation of the branch of 
the Vine that had been disbudded could not therefore furnish any proof of the descent of the sap from 
the apex of a plant to its roots, while growing and in full possession of its vitality. 
“ Circulation of the sap” was the term by which our forefathers attempted to express a series of 
movements that they could not comprehend. Circulation proper, implies a motion corresponding in its 
principle with that of the blood in man and animals, or one which may be represented by the flow 
and return of water through the pipes of a hot-water apparatus. But we ask, can any one of us, who 
has carefully observed the phenomena of vegetable growth, suppose that they afford evidence of a 
regular upward and downward flow of the vegetable fluids. We may never be permitted to discover 
the precise course, nor the exact vessels and cells through which they pass and are elaborated; but 
perhaps we may not be far from the truth if we admit, to a very great extent, the theory of the late 
Thomas Andrew Knight, so far at least as it applies to the channels and course of the vital fluids. 
The raw sap absorbed by the roots ascends through cells of the sap-wood (alburnum) in trees, or 
through cellular tissue in vegetables; it enters the leaves, partially exudes as water through the 
transpiratory pores, undergoes due laboration and change in appropriate cellular tissue, and then in 
the state of cambium , or proper juice, passes downward and through the liber or new bark ; and 
thence is conveyed laterally through the medullary processes, termed by Mr. Knight, “ convergent 
rays or layers,” till it reaches the central medullary sheath. In its course all the specific aromatic, 
gummy, resinous, or saccharine principles are developed, and duly deposited ; and thus the sap from 
the roots performs all its natural offices, being entirely conveyed and applied to all parts of a plant, 
depositing the several products of elaboration, but not in any degree returning back into the roots as 
sap, otherwise than as a niitrimental matter suited to the requirements of the radical tissues. 
Such I believe to be the substance of Mr. Knight’s theory, to which modern discoveries may have 
added some facts connected with the absorption of carbonic acid and solutions of silica, potassa, and 
other inorganic bodies laborated in the soil. Much remains to be adduced concerning the processes of 
vegetable chemistry, but on the subject of the sap’s course I think that the view embraced by Mr. 
Knight is in every way luminous and comprehensive. 
ON CLIMATE. 
By E. J. LOWE, Esq., F.R.A.S. 
X 
W E shall now bring under notice those local circumstances which influence the climate of a locality. 
Towns raise the temperature of the immediate neighbourhood, because the walls of the houses 
absorb a large quantity of caloric during the day, which they give out again at night. In consequence 
of towns being warmer than the surrounding country, no dependence can be placed upon the observed 
direction of the wind near them; for if on the west side we find a north wind, it is not uncommon to 
observe one on the east side coming from the south ; and indeed it frequently happens that in different 
parts of a town the wind is blowing from almost every point of the compass, for the temperature 
being warmer in the interior, and consequently its specific gravity lighter, cold heavier air will rush 
from the surrounding country into the town. Therefore, with our increase in buildings, we make the 
climate milder, and also change the direction of the currents of the air. The next great alteration in 
temperature is produced by draining swamps, fens, and morasses ; and the third by the felling of large 
woods, such as those in North America, all which are accomplished by the labour of man, and each 
tends to temper the climate, for changes produced either by the draining of swamps, or the clearing of 
large forests of trees, even at very great distances from us are felt in a greater or less degree, and the 
effect around those places near where they take place is very sensibly perceived, as in Canada, where 
the climate is rendered much milder. 
Mountains have great influence over winds, and it is natural that they should when we consider 
that the great bulk of the air is near the earth’s surface ; therefore they must act as impediments. 
The daily average rate of the wind at Greenwich, between October 1849 and March 1850, varied 
from 70 to 155 miles. It will thus be seen that the rate of movement of the wind varies very con- 
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