THE FLORAL WORLD AND GARDEN GUIDE. 333 
heat than is really necessary for the exclusion of frost and the 
maintenance of a dry atmosphere. Even with one house only, 
much can with a little management be done to place these two 
classes of plants under conditions most conducive to their health. 
To separate the plants into two distinct groups, and put the hard- 
wooded things at one end of the house, and the soft-wooded things 
at the other, would answer very well so far as the health of stock 
is concerned, but it is not desirable. The appearance of the house 
would be so unsatisfactory, that there would bea very great diffi- 
culty in tolerating the arrangements for any length of time. The 
only arrangement that can be recommended, is to place all the 
plants requiring a free circulation of air about them upon the central 
stage in span-roof houses, and upon the back stage of lean-to’s; 
and the others upon the side stages. When this is done, air is to 
be admitted by means of the ventilators in the roof only. The 
plants on the side stages will have quite as much air as they will 
require, without beiug exposed to cold currents, whilst those on 
the high stage will enjoy that free circulation amongst them so 
essential to their health. 
The ventilation and heating of the greenhouse are points of 
prime importance ; nevertheless, it is a matter of extreme difficulty 
to offer advice of real practical service to those who are in the most 
need of it. It is impossible to allude to them otherwise than in a 
general way; and inexperienced cultivators have necessarily con- 
siderable difficulty in applying to their own case directions of a 
general character. That air is essential to the health of plants is 
generally known, but the knowledge is often not turned to such 
good account as it might be. Instead of the ventilators being 
opened when air can be admitted with advantage to the structure, 
they remain closed for weeks together, because it is feared that the 
temperature will be reduced so much that the plants will suffer. 
As a matter of fact, the ventilators should be opened every day 
when there is neither rain, frost, nor fog. The extent to which 
they ought to be opened, and the length of time they should remain 
open, must be determined by the cultivator. Air should, however, 
be admitted as early in the day as possible, and the ventilators 
closed by two or three o’clock, to prevent the temperature falling 
too low. The temperature of the structures referred to may range 
from 35° to 45°, and with sun-heat it may be allowed to rise to 50°, 
without its being considered necessary to open the ventilators to an 
undue extent, or allowing them to remain open until late in the 
afternoon. On occasions when it is impossible to admit air without 
the temperature being reduced below the proper point, a fire should 
be started a short time before the ventilators are opened, and be 
kept steadily burning until they are closed again. During long 
periods of dull and rather damp weather, a fire should be hghted 
once or twice a week to dry up superfluous moisture, and the house 
be ventilated at the same time to allow the vitiated air to escape, 
and thus ensure a thorough change in the air of the house. In the 
matter of keeping out the frost, the weather must be closely studied, 
and when it is feared that a sharp frost will be experienced in the 
November. 
