NOVEMBER. 325 



much the escape of heat during cold nights or sunless weather, as every 

 body knows who possesses even a handglass. So far concerning provi- 

 sions for retaining the heat, and they may be made as perfect as possible 

 if due regard is also paid to the means of thoroughly ventilating, which 

 is the next necessity we shall notice. It is obvious that these must be 

 sufficiently abundant to admit of the atmosphere being reduced in hot 

 weather to the same temperature with that without. This cannot be 

 accomplished by means of a few trap-doors at top and bottom ; these 

 are useful in their proper places, but in the case under consideration, 

 where the object is to render the effect of the enclosing altogether 

 nugatory, the system of ventilation must be wholesale, and at the same 

 time simple and easily moved. The width of the case should not be 

 greater than is necessary for practical utility and convenience, or the 

 hght will become too much diffused in passing to the trees. 



There is another desideratum w^e must not lose sight of; while we 

 make provisions for accelerating the growth of the trees in summer w^e 

 must remember that they will produce the same effects in winter, 

 unless other means are provided to counteract them. Such a 

 consequence would be very detrimental in prematurely exciting the 

 trees, and the only way in wdiich it can be effectually prevented is by 

 shading. The ease, however, with wdiich this can be accomplished 

 is of itself a strong recommendation to the system proposed, as it is only 

 necessary to cover a portion of the front glass with thin whitewash ; 

 this will in great part be worn off by the spring rains, and what remains 

 can be easily w^ashed away, securing at the same time a thorough 

 cleansing to the glass. 



Having now gone over the principal requirements of a means of 

 protection, w^e will compare our results wdth the descriptions of the plans 

 adverted to in page 260 (present volume). The glass wall of Mr. Ewing 

 fails from its w^ant of the absorbing medium to collect and retain the 

 heat, as the sun's rays, or the greater part of them, must pass quite 

 through the structure into the earth on the opposite side. Mr. Ewing 

 l:as very sensibly (in page 80) refuted one objection he says has been 

 brought against the glass w^alls, namely their being cold in winter. 

 This, in my mind, is one of the best points in their favour. I\Ir. Ewing 

 remarks that the time since the introduction of his glass walls has been 

 too short to test them. He speaks tolerably — and only so — of the 

 example in use at Bodorgan ; and it is but just to give him credit for 

 apparent candour and moderation. It would be conferring a benefit 

 upon us if other gardeners who have tried it or seen it in use w^ould 

 give us the benefit of their observations as to the results — present and 

 prospective. 



I cannot, however, dismiss them without in justice complimenting 

 ]\Ir. Ewing upon the very elegant appearance they must have if 

 extensively carried out, and I would not discourage the idea of still 

 trying them. Something might be done by hanging black curtains up 

 behind the trellis in the spring until the leaves were nearly full grown. 

 The fact of a flatly trained tree being able to expose both its sia-faces to 

 the light of day may probably ensure an amount of elaboration which 

 cannot be obtained in trees against a wall, and which may be a counter- 



