e, can be seen instances suggesting
the evolutionary process; these would be more common but for the number
of connecting links which have dropped out in the great struggle for
existence.

CHAPTER III

DIFFICULTIES TO OVERCOME

Some of the difficulties which the cultivator of Orchids has to contend
against arise from the fact that his houses have to accommodate plants
which have been brought from widely separated countries, or from
different altitudes in the same region. They therefore require very
different cultural conditions, especially in the matter of temperature.

Consideration of the climatic conditions under which the plants are
found growing in their native habitats is very helpful to all engaged in
Orchid culture. Many problems have already been worked out by the
experience of cultivators, but some of the conclusions have been arrived
at only after costly failures. In the early days of Orchid culture,
before the advent of the modern Orchid house with its improved methods
of ventilation and means for the promotion of humidity, the great
mortality among cultivated Orchids was caused by excessive heat and
drought. Even at the present day more mischief is done by excessive heat
than by cold treatment.

CHAPTER IV

STRUCTURE OF THE ORCHID HOUSE

So far as the improvements in present-day Orchid houses are concerned,
these are not due to the imagination of the horticultural builder, but
to the experience of the Orchid grower. It is owing to him that the
old-time glass sides, with their hinged ventilators on a level with the
plants, and many other harmful arrangements, have been abandoned.
Moderately low, span-roofed houses, extending north and south for
preference--although the aspect does not seem to be of vital
importance--are the best, the sides being wholly of brick, and also the
ends of all but the large houses, in which the upper part may be formed
of wood and glass.

The top ventilation should be admitted through ventilators placed at the
highest point of the ridge, and they are usually worked by a continuous
system manipulated at one end. The lower ventilators should be small
ones fixed in the brick-work at the sides of the house, and they may be
arranged to be regulated from the outside, or by means of rods attached
to the flaps on the inside and reaching to the path, being carried
beneath the staging. The natural earth is the best base for an Orchid
house, and open wood-work trell