138 GREENHOUSE CONSTRUCTION AND HEATING. 
this it will be plainly evident that the rails, etc., must 
be at least twice the length of the structure, if not more. 
In fact, in order to obtain satisfactory results, in market 
garden work, at any rate it is advisable that the plot of 
ground fitted with rails should be three times the length 
of the glass roof, in order to provide for a suitable 
rotation of crops. 
I must confess to being unable to perceive the utility, 
or rather the real importance, of this class of house in 
the first instance, but a little consideration quickly showed 
‘that the system possessed important advantages, and 
like other really good things, undoubtedly improves on 
acquaintance. One of ‘the best uses that such structures 
can be put to, and the one that first commended the 
idea to myself, was that of sheltering a batch of chry- 
santhemums, planted outside, after a summer crop of 
tomatoes was over. It will readily be seen that it is only 
necessary to plant out a batch of young “mums” of 
suitable varieties in the next plot (within the rails) in the 
spring or early summer, and when these require protection, 
say at the end of September, and the ‘‘toms”’ are over, 
the house only has to be pushed over—which half-a-dozen 
men can easily do in a few minutes, by the way— 
to accomplish the desired object. In the spring the house 
may be pushed over on to plot No. 3, which may be planted 
with tomatoes again, the chrysanthemums being grown this 
season on the plot occupied by the tomatoes previously, 
and soon. Again, a number of Tea or H. P. Roses may 
be easily forced by merely running the house over them 
in the early spring, after a late crop of tomatoes on the 
next plot, or even after the ‘“‘mums” are over. 
