FRUIT AND KITCHEN GARDENS NEAR PARIS. 



213 



the case will appear evident from an inspection of Bouguer's 

 table of rays reflected from glass. According to this, the ave- 

 rage amount of rays reflected from glass at various angles of 

 incidence from 1° to 87^°, or, we may say, from morning to 

 night, is upwards of 22 per cent. This calculation is on the 

 supposition that the roof is all good glass. But an additional 

 privation of the rays of light must be taken into account, in 

 consequence of their total obstruction by the rafters, &c. ; and 

 sooty laps have no small share in producing obscurity. Alto- 

 gether we may reckon that, in the course of the day, vines under 

 a glazed roof are deprived of more than 30 per cent, of the rays 

 of light which they would enjoy if growing in the open air. 

 This privation must weaken the constitution of the plants, espe- 

 cially when they are year after year subjected to it. 



I do not suppose any one ever saw grapes badly coloured on 

 the open wall, provided they at all approached the state of 

 ripening. When yet sour, they may be seen as black as sloes ; 

 and whether the border is rich or poor, or the fruit exposed or 

 partially shaded by the leaves, still the colouring is good, if the 

 climate is only sufficient to bring the fruit to the stage of growtli 

 in which the colouring process is effected, and although too cold 

 for perfect ripening. The superiority, as regards colour, of grapes 

 on the open wall, may therefore be fairly ascribed to the free 

 action of light on the foliage. 



The influence of light, however, goes much farther than the 

 mere colouring of the fruit. By it the constitution of the whole 

 plant is affected, from the foliage to the very extremities of the 

 roots : the latter, in fact, cannot long continue to be produced 

 unless the leaves effectually elaborate sap, and this they cannot 

 do without free light and air. Even in this country vines grow- 

 ing in the open air maintain their roots in any soil that is not 

 excessively bad ; but with all appliances, how generally do they 

 fail in borders when their tops are kept under glass ! There the 

 heat may be well regulated, greater perhaps than out of doors, 

 but not greater than where the vine lives for centuries, and a due 

 supply of moisture may be afforded ; but the natural constitution 

 of the plant becomes impaired for want of sufficient light ; and 

 sometimes to such an extent that, with a little mismanagement 

 in other respects, the vine is scarcely able to bear fruit at all. 



From the above remarks it may be inferred that M. Berg- 

 mann's plan of alternately forcing and exposing his vines is 

 highly advantageous. Were it not so, he would not likely be 

 at the trouble to move his glazed structure annually. I have 

 endeavoured to explain the principles on which, as it appears to 

 me, the merit of the plan rests ; that is, the beneficial influence of 



