122 GREENHOUSE CONSTRUCTION AND HEATING. 
glass—just enough to break the glare of the sun and prevent 
any scorching of the petals or leaves. This rough and 
ready method is adopted to a considerable extent in 
nurseries, where as a rule great particularity is not 
required. Ordinary lime-wash is frequently employed for 
this purpose, but though suitable enough in other respects it 
is open to the objection that it has an undoubted tendency 
to eat into the surface of the glass and destroy its brightness 
and transparency. It will, however, frequently ‘‘ stick” 
if the lime is fresh, when hardly anything else will. A 
wash made with ordinary whitening to the consistence of 
cream, with a little milk, dissolved size, or oil added to 
increase its adhesiveness, is less objectionable than lime, 
and being whiter, looks better on the houses. A mixture of 
flour and water (not paste), with a little whitening added, 
possesses the advantage of becoming semi-transparent when 
wet, and therefore of obstructing less light when the shade 
is not required. The preparation known as “summer 
cloud,” which is of a pale green colour, is also very 
suitable for the purpose under consideration, and is put 
up in convenient tins and easily applied. 
But the great disadvantage of all these permanent 
shadings is that they obstruct the light and darken the 
house just as much when the shade is not required—that 
is, in the early mornings and evenings, as well as on wet 
and dull days—as at other times, and the tissues of the 
plants are thus weakened and rendered less able to endure 
the fierce rays of the sun when they do come. Now 
light strengthens and invigorates plant life of almost all 
descriptions, and the more they receive, and the fuller 
it is, the better. All that is required is just a light screen 
