May, 1915.] THE ORCHID REVIEW. 139° 
CALENDAR OF OPERATIONS FOR MAY. F| 
By W. H. Wuirte, for many years Orchid Grower to the ' 
late Sir ‘lrevor Lawrence, Bart., K.C.V.O, 
EMPERATURES.—Now that the amount of daylight has increased,. 
the majority of the plants are growing and rooting freely, and the 
night temperatures, as maintained by fire-heat, should be advanced a few 
degrees—the East Indian house from 65° to 70°; Cattleya, 60° to 65° 
Intermediate house a few degrees less; Mexican, about 60°, and the 
Odontoglossum or Cool house about 50°. The higher temperatures should 
be maintained whenever the external air stands at about 50°, but when colder 
the lower one given is preferable. When finishing up for the night those 
in charge of the fires may be weatherwise enough to foresee what the 
weather is likely to be, and so be able to regulate the heating apparatus,. 
and the ventilation of the houses, that the temperatures in each division 
will be about correct in the morning. It will not be advisable to employ 
artificial heat in the Cool houses except when early morning frosts are 
imminent, and then the pipes should be made only just lukewarm, for 
should the atmosphere inside become too warm by this means, the plants: 
might suffer, and insect pests would make their appearance and multiply 
rapidly. Unless absolutely necessary, use no fire heat in this division, and 
the plants will be all the better without it. In the day-time, as mentioned 
in last month’s Calendar, there will still be considerable variation in the 
temperatures; on dull, wet days the higher temperatures prescribed for 
night should be maintained, but when the weather is warm and bright a 
rise of several degrees by sun-heat will be beneficial ; in fact as regards the 
warmer divisions, it matters little how much the rise in temperature by 
sun-heat may be, provided there is sufficient ventilation afforded to 
balance it. 
SUMMER QUARTERS.—Towards the end of the month the following 
plants, which have been wintered in the Intermediate house, may be 
removed to a cooler and more airy house, and the warmest part of the 
Odontoglossum division will be a very suitable place for them for the next 
six months. These include Lelia harpophylla, L. pumila, L. prestans, 
L. Dayana, Dendrobium infundibulum and Jamesianum, Odontoglossum 
Krameri and O. nevium, Miltonia vexillaria, and any of its hybrids as they 
go out of bloom, also M. Phalaenopsis, M. Endresii, and the distinct 
M. Schrcederiana, which also winter best in a light position in the 
Intermediate house. During summer they prefer the Cool house. So 
soon as the day temperature of the Cool house rises on most days to 60°, 
without the aid of fire-heat, it is time for them to be shifted from their 
