204 
ON THE AGENCY OP SOLAR LIGHT. 
volume of atmospheric moisture is maintained by the glass, which has no existence 
in the open air : the situation, therefore, of a plant is rendered unnatural ; and, 
although the knowledge of the native habitats, and of their concomitants, must be 
essentially useful, as affording the basis of analogical reasoning, still, a vast deal 
must depend upon the observation of the gardener, and his adroit readiness to seize' 
at once upon facts as they present themselves to his view. General features which 
are observable in nature, ought to be attentively regarded ; thus, as is observed, 
plants which " are never subjected in the native localities to the immediate influence 
of solar light " ought not to be placed in a situation where they constantly receive 
the most powerful rays of the sun (113), but the particular effects which attend 
an artificial mode of treatment, must be observed with accurate minuteness. 
Plants exposed to the " skyey influences,' 1 be they surrounded, and buried, as it 
were, by underwood, in the deep recesses of forests and drundles, have still freedom 
of exposure to atmospheric agency, without the intervention of a transparent roof. 
But with us, in our glazed stoves, and surrounded by the natives of climates widely 
remote from each other, they have to conform to their new situation, and what is 
perhaps of greater consequence than it is generally thought to be, they have to 
support the influence of an atmosphere charged with the gaseous transpirations of 
other plants, which may be extremely pernicious. Upon what other ground can 
we account for the failure of the hardy heath tribe, unless it be indulged with an 
abode prepared exclusively for it ? All greenhouse plants like air, a due supply of 
water, cleanliness, and correct attention ; but the heaths, and some other subjects of 
extremely hardy and healthy habits naturally, droop, sicken, and fail, if they be 
made tenants in common with any other tribes. It may be said, that heaths and 
their congeners are 44 nriffy," because they are impatient of water, of wind, and of 
the full south sun ; that with care, and attentive regulation they might, and 
would, succeed among other plants. We grant the point, and admit that they 
might exist, as they do in parlours, during two or three seasons ; but has ever 
any one seen a heath in full verdure, in the plenitude of health, so situated, growing 
and blooming for a succession of years ? Such an exception may have occurred, 
but has rarely been witnessed. 
Light acts powerfully upon plants at the different stages of their progress ; the 
fertility of a vine depends mainly upon the solar direct ray operating upon the 
foliage during the growth of the fruit-bearing wood, but the fruit itself will swell 
to the greatest perfection when shaded by the foliage. Light is instrumental in 
promoting all the functions of the fruitful organs, but it operates inimically upon 
the expanded flower. Thus, if a blowing plant of Streptocarpus Rexii be exposed 
to the direct ray, the blossoms will be seen to shoot off, and become pendent on 
the pistillum, within a day or two after they have expanded. In the shade, on 
the contrary, we have frequently retained a plant in full flower, on a mantel- 
shelf, for a month, every individual blossom remaining expanded, and to all appear- 
ance perfect, for more than a week. Every fact proves that information upon native 
