CULTURE OF IPOMCEA LEARII. 
pointed. It is to the carbonic acid, and the aqueous vapour held in solution, that 
we must refer : the first acts directly upon the foliage ; the second acts indirectly, 
in the form of rain, or dewy moisture — agencies which do not form any part of the 
subject now under investigation. Whatever tends to decompose air by the abstrac- 
tion of oxygen, deteriorates it, as we have seen ; but is there any reason to suppose 
that plants decompose air ? If they do not, then air is to be considered as a vehicle 
or medium only calculated to receive and transmit gaseous matters. 
In this view of the subject, we are assisted by the evidence furnished by the 
experiments of Mr. Ward, Air so impure as is that of the immediate vicinity of 
Wellclose-square is deadly to vegetation ; but the portion which permeates through 
the soil of his cases, or the almost sealed glazing of his subterranean fernery^ is 
purified by filtration, and the plants are verdant as in their own rural habitats. Do 
not these facts teach us, that we are too liberal in our applications of air ; and would 
not the major part of our tender plants thrive equally well with closed glasses, and 
even with puttied laps ? Moisture would be more regularly maintained and dis- 
tributed ; the most brilliant light would be better supported, and vegetation be con- 
sequently rendered more luxuriant. We have seen a fig-tree in full foliage, removed 
from a stove to the open air, which, within twelve hours after its removal, had not 
a single leaf alive. , 
Air checks, but does not harden ; it ripens the wood, and therefore promotes 
bloom : hence its great use to geraniums, heaths, and many hard- wooded tribes. 
But it is inimical to luxuriant growth, and therefore should not be permitted to 
enter any house in the form of a current, especially as it is a known fact, that plants 
support a much higher and lower temperature in close situations without injury. 
Let experiments be widely instituted in order to ascertain the agency of air ; for, 
after what we have witnessed, it becomes a question whether, as a general thing, 
we are not at infinite pains to ventilate our houses, with no other result than the 
incurring much trouble without any corresponding advantage. 
CULTURE OF IPOMCEA LEARII. 
It is a singular fact, and one which reflects high credit on the floriculturists of 
this country, as well as proves, to a demonstration, the 'comparative perfection to 
which the art has been brought, that, notwithstanding the ungenial nature of our 
chmate, and the many difliculties which the grower of exotic plants must necessarily 
have to encounter in consequence thereof, multitudes of species attain a finer and 
more splendid condition under the treatment here afi*orded, than in"their native state. 
Out of m.any plants that might be adduced in support of this statement, we 
select one that will best serve our present purpose, as it will give occasion for a 
few hints on its culture. This is Ipomcea LeariL In Ceylon, where it was found 
