64 



wall, communicating with this perforated 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 alto- 

 gether : 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, suffi- 

 cient moisture was kept up by syringing the walls and 

 pipes, wetting the pathway, and by the use of evapor- 

 ating troughs, placed on the metal pipes, and kept 

 constantly filled with water." 



In another communication published in the work 

 already quoted, f after alluding to the now well-known 

 garden truism, that a comparatively low night tem- 

 perature is indispensable to the maintenance of vigor- 

 ous growth in plants of all kinds, I have advocated a 

 more extended adoption of the practice of night cover- 

 ing hot houses, as a means of permitting the low night 

 temperature required, and at the same time securing 

 the plants against the extreme cold to which they 

 would thus be sometimes liable. From the changeable 

 nature of our climate, there is some difficulty in appor- 

 tioning the degree of applied heat, so as to suit exactly 

 the requirements of the plants in these respects ; and 

 it is especially difficult to maintain with certainty the 

 low degree of night temperature which would be desir- 

 able, and at the same time avoid risking the safety of 

 the plants, through a sudden declension of the tempera- 

 ture of the exterior air. At present this difficulty has 

 to be met by extraordinary care on the part of the 

 gardener, and often by serious encroachments on his 



t Ib. vol. II. p. 29. 



