276 



VENTILATION. 



their due proportion of these elements, 

 for the sluggish motion of the air in a 

 hothouse is so different from the natural 

 atmosphere, which is always in motion, 

 more or less rapid, both horizontally and 

 vertically, that the plants may not be able 

 to appropriate their due share of atmos- 

 pheric food, the air not coming fast 

 enough in contact with the leaves and 

 other surfaces of absorption. The advan- 

 tages to vegetation of brisk motion in the 

 air, therefore, will be obvious." — Mr 

 Scott in Jour, of the Hort. Soc. 



Every cultivator who has studied the 

 subject now admits the necessity of warm- 

 ing the external air by some means or 

 other before it is admitted to come in 

 contact with the plants. The late excel- 

 lent president of the Horticultural Society, 

 Thos. A. Knight, was amongst the first to 

 direct attention to this subject, (vide sec- 

 tion Pits,) but few followed his example till 

 of late years. One of the most rational 

 plans to effect this desirable object, with- 

 out sacrificing the natural humidity of 

 the air, is detailed by Mr Thomas Moore, 

 (author of a useful treatise on the cucum- 

 ber,) in a paper in " The Journal of the 

 Horticultural Society." " I recommend 

 warming the external air," he says, " be- 

 fore admitting it to the plants, by a plan 

 which will be explained by the annex- 



Fk- W) ed dia S ram > % 



359. The main 



point which this 

 plan was in- 

 tended to secure 

 was this, that the 

 cold air should 

 pass directly 

 over the surface 

 of the heated 

 water in a tank 

 provided for 

 supplying bot- 

 tom heat to the 

 cucumber pits; and by passing over 

 this surface, it was supposed that it would 

 not only be warmed, but so far charged 

 with moisture as not to abstract any from 

 the succulent foliage and stems of the 

 plants, but rather to furnish them with a 

 source whence they themselves might 

 draw part of their supply. This plan 

 was entirely unconnected with any scheme 

 for securing motion without admitting the 

 external air; but it is obvious that both 



might be combined, as in the following 

 Fia- 360 diagram, fig. 360, 



s ' ' which also repre- 



sents an improve- 

 ment on the ori- 

 ginal plan. In 

 this arrangement 

 it will be seen that 

 the cold external 

 air is supposed to 

 pass through a 



... heated chamber 



JiJpJJ* separate from the 

 tank, but admit- 

 ting of communication for the purpose of 

 supplying moisture if necessary. Thus the 

 external air may be warmed either with or 

 without being moistened before it reaches 

 the plants inside the houses, or the mois- 

 ture may be directly admitted from the 

 tanks by other means, in the exact quantity 

 required at any particular stage of growth. 

 The advantage gained by this plan is a 

 greater command over the moisture of 

 the atmosphere, though, in a forcing- 

 house, such a power would seldom be 

 required to be put in practice." 



Mr Moore, in the same communication, 

 mentions a plan invented by Mr Leaf's 

 gardener, which "consists in passing a 

 zinc pipe, thickly perforated with small 

 holes, from end to end of the vinery, and 

 exactly beneath the range of hot-water 

 pipes which heat the structure. In the 

 outer wall, communicating with this per- 

 forated pipe by means of a kind of broad 

 funnel, a register-valve is fixed, by which 

 the admission of air can be regulated with 

 the utmost nicety, or the supply be shut 

 off altogether. This valve is fixed a little 

 below the level of the perforated pipe. 

 The action of this contrivance was evident 

 enough from the motion communicated 

 to the foliage of the vines ; and its effects 

 were apparent in the unusually healthy 

 and vigorous appearance they bore until 

 their period of ripening. In this case, 

 sufficient moisture was kept up by syring- 

 ing the walls and pipes, wetting the path- 

 way, and by the use of evaporating 

 troughs placed over the metal pipes, and 

 kept constantly filled with water." 



The first great reform in ventilating 

 forcing-houses was brought about by the 

 late Mr Atkinson, and will be understood 

 by a glance at the section, fig. 361, which 

 shows one of the houses in the Horticul- 



