lumns under the
rafters, which are indispensible under a straight roof of considerable
span, to prevent its settling down, and the opening of joints in glass
and wood work, admitting the cold air from without.

A good proportion for a grapery or conservatory, is twenty feet in width
by fifty feet in length. We think the width should never be much less
where the roof is of double pitch. Single pitched houses should not
exceed sixteen feet in width.

Mistakes are frequently made in the erection of structures for the
growth of plants which, notwithstanding all the skill and art of
experienced gardeners, render it impossible to arrive at satisfactory
results. One of the most common of these is the excessive height of the
roof. Men of experience in the construction and use of glass houses,
have satisfied themselves that the lowest elevation which the uses and
purposes of the building will admit, is the best. The difference in
temperature between the floor and roof of a house twenty feet in height,
will vary from ten to fifteen degrees. It is obviously desirable that
there should be as little difference as possible in the temperature of
the air on the ground, among the lower parts of the plants, and in the
upper regions of the house. The nearer we can approach an equilibrium,
the better success will attend our efforts. Nurserymen generally, and
sometimes other cultivators, understand this, and they build their plant
houses with roofs of low pitch, affording scarcely room to stand upright
within them. Their plants are thus brought near the glass, and they grow
stocky and firm, presenting quite a different appearance from the
attenuated specimens frequently met with in private establishments.

HEATING.

The proper heating of Horticultural buildings being an important feature
in their general management, and an essential condition of their
success, we shall consider the subject at some length, availing
ourselves of the practical experience of others, as well as of the
knowledge we have acquired in our own experiments and practice.

Hot air stoves have been so generally condemned and discarded as a means
of heating glass structures, that we shall not discuss their faults or
merits, but confine ourselves to heating by flues, steam, and hot water
in pipes and tanks.

FLUES.--Flues have been generally used in heating for many years, and
although the method is rude, imperfect and unsatisfactory, they possess
certain advantag