• 1870. ] 
THE ART OF FORCING FRUIT AND FLOWERS.—II. 
81 
when a strong young gi’owth is the main desideratum, tlie sun having moderate 
power for warmth, moisture in the form of vapour—atmospheric humidity, in 
fact—must be fairly supplied in proportion to the natural and artificial warmth. 
Between the middle of February and the end of March, the structure may be 
closed, as regards air-giving, as soon as the sun has passed the meridian, and 
thus a considerable amount of natural warmth may be stored, with all its invigorat¬ 
ing infiuences, and the necessary temperature may be thus maintained away into 
the night. The humidity already suggested becomes thoroughly incorporated 
with this warmth, and with what fresh air was admitted in the early part of the 
day, and thus the most natural and favourable condition of the atmosphere is so 
far ensured. This growing temperature is gradually carried away into the night¬ 
time, under the cooling influences of which it expends itself, and holding the 
humidity in its grasp while the temperature descends to a minimum, deposits it 
by a process of condensation in myriads of particles on leaf and branch, bathing 
all their surfaces in almost imperceptible moisture, aiding plant and leaf alike in 
their effort to collect fresh energy for the following day. Thus the most natural 
growing conditions are assured under a strictly artificial regime. 
But having got thus far, I should not be dealing honestly with the subject, 
did I omit to draw attention to another consideration which a superficial observer 
might fail to discern, but which in actual practice exerts a very material influence 
in connection with all successful forcing. I allude to a properly balanced 
temperature throughout the whole twenty-four hours. Thus, for instance, the 
mean heat attained to during the afternoon, when the structure is deprived of air, 
should to some extent be regulated by the range of temperature which existed 
in the early morning, this being, to a great extent, a key to what it fell to 
during the preceding night. However bright the day may be, or however high 
the sun unaided may be capable of raising the temperature, at this youthful 
period of the plant’s growth, it is not desirable that the maximum by day should 
exceed by more than 20° the early morning temperature. Thus if a temperature 
of 60° is indicated in the early morning, it will amply suffice if 80° be attained 
in the afternoon; if 70° in the morning, then 90° as the day wears, &c. I 
am now speaking of the spring season. This formula may be increased in a well- 
studied ratio as the summer comes on, and the young growths, advancing to 
maturity, provide a larger amount of organisable material to meet the increasing 
wants of the crop. With the advent of autumn, vegetation being hardened by a 
summer’s exposure, we may safely make use of our knowledge regarding the great 
amount of heat which tropical vegetation requires. The wood being formed, 
and the fruit in process of ripening, it will then be proper, with a little less 
humidity, to allow a maximum temperature of 96° or 100°. 
If there is one evil more than another to which gardeners do not give suffi¬ 
cient weight in forcing operations, and which demands our most earnest atten¬ 
tion, it is that of allowing excessively high night temperatures. This is a point 
