VENTILATING FORCING-HOUSES. 79 
be secured by means of sash at the peak alone, thus obvi- 
ating the danger of currents of cold air which arises when 
there are ventilating sashes in both the sides andtop. In 
very large houses, particularly in those of the shed roof 
pattern, it may be necessary to place ventilating openings 
in the walls, more especially on the back or high side of the 
house. Ventilating openings should be removed as far as 
possible from the plants in order to reduce the danger of 
cold draughts to the utmost. 
Particular care should be taken with the ventilating dur- 
ing dull, cold weather, when the plants become soft and are 
very quickly injured by draughts. It is not necessary to 
ventilate primarily for the purpose of securing fresh air, but 
to regulate the temperature of the house. When the house 
becomes over wet and close, it is often necessary to ventilate 
for the purpose of drying it out. The larger the house, the 
less, as a rule, is the necessity of ventilating. 
Houses are shaded to prevent the sun from scorching the 
plants. The shading is supplied by coating the glass with 
some white covering, like whitewash. The necessity for 
shading may be largely obviated by not allowing the plants 
to become over-vigorous, sappy, and soft. The greatest 
danger from sun-scald occurs after a spell of dark and wet 
weather. It is then essential to keep the house rather cool 
when the weather brightens, and it may be necessary to 
shade it. Plants which are suffering from root-galls or other 
disease of the roots, or those which are growing in very 
leachy soils or on very shallow benches, may have to be 
shaded in order to check the evaporation from their tops 
and thereby prevent them from wilting. Many plants thrive 
best under shaded roofs, but amongst the forced vegetables 
there is only the English or frame cucumber which appears 
to thrive best under a tempered light. This plant was 
developed in the humid and soft climate of England, and it 
seeems to be impatient of our violent suns; yet it may be 
made to withstand the sun if grown rather slowly. 
For plants which require permanent shading, a paint 
