GENERAL TREATMENT IX SPRING AND SVMMER. 



299 



less. Air must also be admitted in fine days in much greater quantities 

 than during the preceding months, and the operation of steaming per- 

 formed every evening during the T^^hole period, and continued as long as 

 there is suflacient heat kept up by fire in the flues ; after ^vhich the 

 steaming must be performed in the morning, by syringing the plants and 

 walls of the house all over, and keeping it closely shut up till the sun 

 raises the thermometer to eighty or ninety degrees, or higher, when air 

 may then be admitted, to reduce it to its usual temperature. By following 

 this process, those pests of all hothouses, the mealy bug and red spider, 

 win be completely destroyed, neither of which can exist in a high humid 

 temperature or atmosphere, but the reverse is the very medium that vdU 

 bring them into existence in swarms. This circumstance, upon the first ap- 

 plication of steam to hothouses, caused an erroneous notion to be attached 

 to that mode of heating, namely, that by it insects were totally suppressed. 

 No such thing is or can be the case where steam is employed, if kept 

 confined in the pipes : it is by its escape from them that this desirable 

 end is eifected ; and though it was only where the practice was followed 

 of opening these pipes and allowing a portion of the steam to enter the 

 house, that the insects were found to disappear, yet the whole merit was 

 set down to the credit of this mode of heating. The same effect had 

 been observed in houses in which the process of raising steam by pouring 

 water on the flues had been followed ; but keeping the atmosphere of hot- 

 houses damp, was at that time rarely thought of, and hence the indifferent 

 success attending the cultivation of tropical plants and fruits when com- 

 pared to that of the present day. The apphcation of water by a pretty- 

 strong syringe upon the plants, answers also two very important ends, 

 viz., the cleansing of them from dust and insects, and also acting as a 

 substitute for wind, which, in respect to giving strength to plants, has been 

 experimentally proved by the late Mr. T. A. Knight, and other vegetable 

 physiologists, to be of much use, particularly to those placed in situations 

 where this natural agent could not act upon them. 



The season for shifting tropical plants extends from the end of Feb- 

 ruary to the end of April, at which period the plants begin to grow, and, 

 consequently, to make fresh roots, which is the most proper time for 

 performing this operation on all plants. This should not, however, l)e 

 deferred later than the end of April, for by that time the plants will have 

 grown considerably, and would thereby experience a great check if dis- 

 turbed at their roots. 



Shifting or re-potting plants is a very necessary- branch of culture, for 

 when we consider that the quantity of eaith contained in a flowerpot is 



