214 
Garden Work 
perhaps, say that a plant “ catches cold ”, at any rate we 
know that their growth is checked, and, if tender, they may 
be killed by draughts. To avoid this we must admit the 
air very cautiously, and at places where it will not come 
into direct contact with the plants before mixing, to some 
extent, with the warmer air of the house. This may be 
accomplished by having ventilators at the apex. When 
the cold air enters, being heavier than the air inside the 
house, it naturally descends, and thus becomes warmed 
in passing through the warm air before reaching the plants. 
Some of the warm air is driven out, and other cold air 
enters, thus establishing a circulation without draught. 
Sometimes, however, it is necessary to admit more air 
than will enter by the top ventilators, especially as spring 
and summer approach. The front ventilators now require 
to be opened. These, if possible, should be placed so that 
the cold air will pass over the hot-water pipes, and thus 
become warmed before reaching the plants. In this way 
an abundant supply of fresh air may be admitted without 
any fear of danger to the plants. The spring is the most 
difficult time of the year in which to ventilate the green- 
house properly. The plants are starting to grow, and the 
young growths are very tender, and liable to be injured 
by cold currents of air. The writer well remembers an 
incident which happened shortly after he started his 
gardening career. It had been a frosty morning, the air 
was sharp and clear, and the sun came out very strongly. 
He was in entire charge of the ranges of houses, one of 
which was a stove, which had been heated in the morning 
to keep up the temperature. When the sun came out, he 
immediately damped down the fires; but still the ther- 
