respirationatthattemperature. A coolhouse orchid may not sur- 
vive at 80° F. because it may respire so fast that the process of 
food synthesis cannot keep up with the rate of re spiration. If the 
night temperature is toohigh during periods of poor light intensity, 
growth becomes weakened, the flowers are smalland dark-colored 
flowers become pale. 
Generally, Cattleyas grow well with a minimum night temperature 
of 60° F. or within a range of 58° to 65° F.. Most growers keep 
the day temperatures five to tendegrees above the night tempera- 
ture during cloudy days and from ten to fifteen degrees higher 
during bright days. 
Light is necessary in the manufacture of food by plants. Aside 
from other factors, there must be sufficient light for maximum 
food production. 
Many orchid growers have a tendency to shade Cattleyas ex- 
cessively. This practice keeps down food production and slows 
growth. A very low light intensity is especially detrimental at 
high temperatures. Such temperatures are conducive to rapid 
respiration and what little food is synthesized in the plant under 
conditions of poor light is rapidly used in respiration. Cattleyas 
receiving too little light have small, thin and weak pseudobulbs. 
The leaves are thin, flop over and sometimes do not expand fully. 
Increasing the light intensity not only promotes a strong, vigorous 
top growth but also improves root growth; food production is 
stimulated and more food becomes available for the proper de- 
velopment of both top and roots. The amount of stored food in- 
fluences flower production and the size, color, and texture of the 
flowers. 
Very high intensities, on the other hand, can reduce the amount 
of chlorophyll in plants. Chlorophyll is the substance that is re- 
sponsible for the green coloration of plants and which enables a 
plant tomanufacture food. WithCattleyas, too much light results 
in yellowing of leaves. 
REGULATING THE LIGHT INTENSITY. Removing shade from the 
glass in winter helps the plants to utilize all available light. The 
shading material ordinarily used is easily washed off by rains so 
that by winter there is hardly any left. Scrubbing may be neces- 
sary where amore permanent type of shade has been used, as 
