158 
ON THE INFLUENCE OF CLIMATE ON PLANTS. 
scorching rays of the summer sun. By this latter mode of treatment, the plants 
will not only be preserved from sudden destruction by the fierce rays of the sun, 
but the generation of mildew, which is well known to prove so fatal to heaths, will 
be in a great measure prevented. Most practical writers on the subject of heath- 
culture, agree in ascribing the production of mildew on these plants to the effect of 
the too-powerful rays of the summer's sun ; and it is recommended to place the 
more delicate sorts in a frame during the summer season, the lights of which are 
glazed with green glass ; removing the latter entirely when the sun is not shining. 
This practice, however, is far more expensive, and certainly not more effectual, than 
that of shading the house in which the plants are kept, for the lights would be 
entirely useless in the winter season ; the plants likewise would not be exhibited 
to advantage in such a situation ; and we reiterate our opinion, that shading is not 
only a useful and important feature, but the most preferable mode that can be 
pursued, in the cultivation of heaths. 
Passing on to the consideration of the effect of light on orange trees, we find 
ourselves involved in a curious and somewhat intricate inquiry. No person who 
has witnessed the orange houses of this country, which have been built for the 
professed and almost exclusive purpose of cultivating orange trees, but must have 
been impressed with the notion that these plants are impatient of light, and 
incapable of enduring a great degree of it. With massive walls of brick or stone, 
on the southern side of which a few windows are generally introduced, and the only 
other light that can be admitted being conveyed through the roof, which is certainly 
sometimes glazed, but elevated to an immense height ; our orangeries have more 
the appearance of gloomy prisons, than repositories for plants. The general heavy 
character of these structures must appear the more extraordinary to the casual 
observer, from the circumstance of most cultivators exposing their plants to the 
open air during that period of the year in which solar light is the most powerful, 
and its action much more continued, and confining them in these dull and dark 
conservatories when light is so much mitigated from natural causes. These 
apparent discrepancies we must confess we are at a loss to reconcile, but there does 
appear to us to be a propriety in not subjecting orange trees to too great a degree 
of solar light, at all seasons of the year ; though we think that most cultivators 
have erred in carrying this principle to the extreme in their construction of houses 
for the reception of these plants. 
Where orange trees are cultivated solely for the production of fruit which can 
be applied to edible purposes, there can be little doubt that full exposure to light, 
at all periods of their growth, is a most important point to be attended to ; but 
such is by no means the object of the cultivators of this country, and if it were, is 
not likely to be attained to an extent sufficient to compensate the grower. It is 
the appearance of the plants — both of the foliage and fruit, for which alone they 
can be esteemed in our collections ; and to preserve the former in a healthy and 
luxuriant state, and at the same time to ensure a profusion of the latter, either too 
