rolled at will. The size of the house varies, of
course, according to the extent of the operations which the grower has
in mind.

The usual type of house is long and rather narrow, varying from 50 to
150 feet long by 18 to 21 or 24 feet wide. In some cases the single
house is constructed upon these proportions, as shown by Fig. 226, with
a gable roof. If it is desired to double the capacity of a house, two
such houses are built parallel, the intercepting wall supporting the
adjacent roof of the two houses, as shown in Fig. 227. A still further
increase in the capacity of the house is often effected by increasing
the number of these houses side by side. This results in a series of 8
or 10 houses forming one consolidated block of houses, each with its
independent ridge roof and system of ventilation. The separating walls
between the several houses of such a block are probably maintained for
the purpose of better controlling the temperature conditions and
ventilation in various houses. If desired, communication from one house
to another can be had by doors.

=Interior structure and position of the beds.=--The beds are usually
arranged in tiers, one above the other, though in some houses the beds
are confined only to the floor space. Where they are arranged in tiers
in a house of the proportions given above, there are three tiers of
beds. There is one tier on either side, and a tier through the middle;
the middle tier, on account of the peak of the roof at this point, has
one more bed than the tiers on the side. The number of beds in a tier
will depend on the height of the house. Usually the house is constructed
of a height which permits three beds in the side tier and four in the
center tier, with an alley on either side of the center tier of beds,
giving communication to all. If the house is very long and it is
desirable, for convenience in passing from one house to another, to have
cross alley-ways, they can be arranged, but the fewer cross alleys the
larger surface area there is for beds.

[Illustration: FIGURE 228.--View in mushroom house (Wm. Swayne), showing
upper bed in left hand tier. Copyright.]

The size of the beds is governed by convenience in making the beds and
handling the crop. The beds on the side tiers, therefore, are often
three to three and one-half feet in width, affording a convenient
reaching distance from the alley. The beds of the center tier have
access from the alley on either side and are us