10 ORCHIDS. 
amateurs, and even by some professional growers. A plant 
is just as unlikely to continue strong and healthy in a 
badly-ventilated house as we ourselves are. Many builders 
of greenhouses are now careful to make arrangements for 
a constant supply of fresh air to the plants at all times, 
and in all seasons. Ventilation, as applied to plants, means 
two distinct things: (1) the regulation of temperature, and 
(2) the admission of fresh air. The former is frequently 
necessary during the summer, and only rarely in winter; 
the latter is necessary at all times. In the construction of 
plant-houses we should always bear these two points in 
mind. By fixing ventilators at the bottom of the house, 
below the level of the pipes inside, the air is compelled 
to pass over the warm pipes before it reaches the plants. 
As a rule, the glazing of houses is rarely so well done as 
to be airtight, and it is therefore seldom necessary to 
have permanent ventilators for the roof. But in well-built 
houses even this is a wise precaution. It cannot be too 
clearly understood, that to grow Orchids well they must be 
supplied with fresh air, which in cold weather should be 
slightly warmed before it comes in contact with the plants. 
When regulating the temperature by means of the ven- 
tilators, care should be taken to avoid anything like a 
sudden change. All the advantage possible should be taken 
of sun-heat. The temperature during bright sunshine may 
rise to 10odeg. or even 2odeg. higher than is necessary during 
dull weather. In the afternoon, the heat of the house should 
reach its maximum, and then fall gradually till the night 
temperature is reached by midnight. In opening the ven- 
tilators, the direction of the wind should be observed, and 
those on the windy side be kept closed, if convenient; 
otherwise the wind is apt to “lick up” the moisture in 
the house. 
