Sept., 1892 . 
THE CULTIVATION OF ORCHIDS. 
209 
there is no question that the most successful results are 
obtained by admitting air freely, not only to cool houses but 
to tropical orchids. In ordinary cases a piece of board eight 
or nine inches wide, and two feet long, sliding m two grooves 
outside the house opposite the pipes, is sufficient for ventila¬ 
tion beneath the stages. During the winter, whenever the 
wind is keen or frost severe, never ventilate, and in very hot 
dry weather it is better to shade well, employ no fire heat, 
damp liberally, and ventilate but little. Without artificial 
heat the temperature may be allowed to rise considerably 
above the maximum temperature given in the table without 
danger, if water is abundantly supplied. For this reason the 
houses may be closed at three or five p.m., according to the 
season and weather, but a little all-night ventilation in the 
height of summer will not hurt tropical orchids, and for 
others it should be the rule at that time of year. 
For shading, the ordinary roller blinds are very con¬ 
venient, as they can be quickly run down or up according to 
the weather. I prefer the material to be stout tiffany, as it 
divides the sun’s rays and so prevents the plants being 
scorched, but does not darken the house too much. Artificial 
shading should only be employed in very bright weather, and 
in the hottest part of the day, to prevent the temperature 
rising too high, as too much shade weakens the plants and 
prevents their growth ripening. 
Most plants are subject to insect pests, although it is not 
often that they do any serious damage, i.e., if ordinary precau¬ 
tions are taken by the cultivator to prevent injury. Thrip is 
one of the worst, especially if the temperature of the house is 
excessive and the atmosphere dry. 
Red spider sometimes, though rarely, makes it appearance 
in a dry corner. The yellow fly, green fly, scale of several 
sorts, and mealy bug attack orchids ; while snails, slugs, 
woodlice, ants, and cockroaches also cause much trouble if 
allowed to become numerous. 
The frequent use of tepid water, and soft soap in very 
small quantities, or weak tobacco water is the best means of 
keeping the foliage clean, applying the liquids with a sponge 
or camel’s hair brush, Green fly and thrip may be destroyed 
by fumigation with tobacco, which should be given very 
moderately on several alternate nights. But I think the 
safest plan is to cover the hot water pipes with the tobacco 
paper, and water that once or twice a day, the steam rising 
from this will destroy all thrip. 
Slugs and snails must be looked after closely, a little bran 
being a good bait for them. It is most annoying, after 
waiting and watching for a spike to open its flowers, perhaps 
for the first time in England, to find one morning that it has 
