ON EXPOSING GREENHOUSE PLANTS IN SUMMER. 43 
expediency, and by no means called for by the nature of things, or conducive to the 
health of the plants so treated. Still there are many who, by their writings, yet 
inculcate the old notion, and others who, in their practice, acknowledge the 
influence of that notion. We are bound, too, to affirm that the aspect of plants 
cultivated by some of the latter class speaks more strongly in favour of the system 
than all- the arguments that have ever been laid before the public. 
We propose, on this occasion, to place the matter in what we conceive to be a 
new light; and while we prove that the objectors to the plan have been generally 
correct, as far as they have pursued their inquiries, we shall also strive to 
demonstrate that summer exposure is in itself useful, and therefore proper, if rightly 
effectuated. 
Without canvassing too minutely the reasons assigned by the opponents of this 
system, it will be desirable just to indicate what are the chief and most potent. 
First, however, it may be better to state the objects supposed to be promoted by 
the plan. It is believed, and most justly, that when exotics pass from their 
dormant state into one of active development, they demand a greater freedom from 
the contact of their neighbours, and to be kept much further apart from each other. 
A larger amount of air and light are also requisite, and these can only fill the 
atmosphere around the plants, so as to act beneficially on their leaves and branches, 
when they stand at some distance from all other objects. But if the collection be 
extensive and somewhat crowded through the winter, this important thinning of 
the specimens can only be made by transferring some of them to the open air. 
Again, plants in houses, it is thought, have an invariable tendency to form long 
and rather weakly shoots, owing to the want of that intensity of solar light which 
they experience in their native regions ; and the absence of that great degree of 
light is also regarded as a prime cause of their too frequent infertility. The 
remedy for such defects is naturally enough looked for in the open air, where the 
largest supply of light which our atmosphere can possibly transmit is, without 
doubtj obtained. 
Further, it is conceived that species which are liable to disease from saturation 
with water while in the house, become less likely to be subjected to that evil when 
there is such a constant drain on them as that which exists in the natural atmo- 
sphere. Others, which suffer from mildew, are supposed to be preserved from its 
attacks when taken from the confined air of a house and placed in a purer medium. 
From such, and additional circumstances which are hardly worth enumerating, 
a necessity has been imagined to exist for placing greenhouse plants in the open 
air while summer lasts ; and the practice, once adopted, has grown into a habit, 
which, though it were shown to be absurd and injurious, could not easily be 
eradicated. 
To the reasons above given, it might be replied that no person ought to cultivate 
more plants than his houses are capable of containing, assuming that the specimens 
were arranged at a stated distance from one another, according to their dimensions. 
