440 PITS AND 



In principle, if we except the iron 

 troughs, this pit does not differ from those 

 in use in the gardens at Dalkeith, erected 

 in 1841; and, from our experience during 

 that period, we can speak in the highest 

 terms of their utility. Our pits are used 

 for cucumbers, with the vaults below the 

 tanks, &c. 



Fig. 611 shows a fruiting pine-pit by 

 the same author, which will be at once 



understood from the following references : 

 a a paths ; b b hot-water pipes ; c perfor- 

 ated copper pipe, by which water may be 

 thrown over the pipes, to promote humi- 

 dity in the house ; d d stone shelves for 

 the growth of strawberries in pots, &c. ; 

 e iron grating over hot-water pipes; / 

 opening for the admission of cold air, to 

 cause the heated air to ascend at the 

 grating e from the pipes at b. 



The Worsley pit, fig. 612. We had an 

 opportunity of examining this pit shortly 



Fig. 612. 



after its erection, the details being kindly 

 pointed out to us by Mr Mitchell, who 

 stated his principle to be, obtaining a full 

 supply of fresh air without the danger of 

 a cold draught ; securing circulation with- 

 out loss of heat ; obtaining sufficient 



FRAMES. 



bottom heat; and, lastly, a supply of 

 humidity in proportion to the internal 

 temperature. The first is attained by 

 opening the upper sash for admitting cold 

 air, which he concludes falls into the pas- 

 sage a, and which, having to pass through 

 the heated vault is in a proper state 

 and temperature to come in contact with 

 the plants. The way of securing the 

 second will be seen by referring to the 

 diagram, in which c is the flow-pipe, d d 

 the return pipes placed in the vault b. 

 As the air in this vault gets heated, it rises 

 through the aperture e into the pit or 

 house. This deficiency is made good by 

 a constant supply of cold air from the 

 passage a. Mr Mitchell calculates that 

 upon the heated air coming in contact 

 with the glass of the roof it gets cooled, 

 and sinks to the passage a, and from 

 thence again into the vault, thus keeping 

 up a constant circulation of air, — of course 

 increasing or decreasing in velocity ac- 

 cording as the temperature in the vault 

 rises or falls, and thus without much loss 

 of heat, as the same volume of air per- 

 forms the revolution. We apprehend that 

 a very considerable improvement might 

 be made here by admitting fresh air from 

 without the house into the vault, regulat- 

 ing this supply by valves or otherwise to 

 suit existing circumstances. No doubt 

 all plants are benefited by motion, how- 

 ever produced, for we find such going on 

 in nature ; and motion produced by me- 

 chanical power, or, as in this case, by a 

 current of unequal heated air, must, to a 

 certain extent be beneficial ; but the same 

 air revolving over and over again in a 

 plant-house is quite analogous to man in- 

 haling the same air over and over again 

 in a closely shut up, ill-ventilated room. 

 Plants derive no small share of their sus- 

 tenance from pure air ; and why should it 

 be denied in cases where it can be so 

 readily afforded them 1 for it is not always 

 convenient to open the top of the lights, 

 in rainy weather for instance, or when 

 snow is falling. We believe that no one 

 will deny that the best point to admit 

 pure air for ventilation, either in the 

 dwelling of plants or men, is at the lowest 

 possible point, and the best for the exit of 

 heated and impure air at the highest part 

 of the building. We would suggest, as 

 an improvement in this otherwise excel- 

 lent pit, the admission of cold air by a 



