GLASS STRUCTUEES AND APPLIANCES. 



101 



understood, wooden roofs contain barely a third of 

 the timber that used to be put into them. In fact, 

 so much has the actual j^roiDortion of timber to glass 

 been reduced, that not a few wooden houses — as 

 they are called — would run the iron ones pretty 

 closely in this matter. The demand for more light 

 to tropical plants has succeeded in reducing the 

 opacity of roofs to the smallest dimensions consistent 

 with sufficient strength and the appearance of per- 

 fect security. In not a few plant-stoves and Orchid- 

 houses the latter has been lost sight of, or not suffi- 

 ciently cared for, and the plants appear in danger of 

 being turned out of doors by the fall of the house 

 at the approach of the first storm. But sufficient 

 strength and stability to look safe are quite com- 

 patible with such a degree of lightness as shall sup- 

 ply the needs of the plants. 



Transparent Glass.— This is of equal or more 

 importance than light framework. All is not gold 

 that glitters, nor is all glass transparent that looks 

 so. Experimental tests of the translucency of glass 

 would prove of the greatest practical importance. 

 There should be some simple method of testing the 

 transparency of glass as there is of measuring the 

 luminosity of gas-light, and the glass should be sold 

 by a transmitting standard. Not a few of the 

 cheaper horticultural glasses are probably not more 

 than half translucent — that is, they only transmit 

 about fifty out of every hundred per cent, that falls 

 on their sirrface. The question of angles of high 

 or low transmission has been discussed under the 

 head of Conservatories. But these points, important 

 as they are, are as nothing to the glazing of plant- 

 stoves or Orchid-houses with clear glass to start 

 with. 



Glass of fair price and good quality is mostly 

 clear. It is the cheap bargains so often offered at 

 clearance sales, or in answer to low-priced adver- 

 tisements, that are to be dreaded, and altogether 

 avoided. A penny saved in such matters as the 

 glass for stoves and Orchid-houses, is a penny — it 

 may be pounds — lost ; and there is nothing pays so 

 well in produce and satisfaction to all concerned 

 as good glass for hot-houses — say, for superior sorts 

 of houses, 26 oz. to the foot, or even heavier. 



Having secured good glass, it is most important 

 to keep it clean by annual or more frequent 

 washings. Nothing is more improvident of the 

 most valuable of all natural forces, light, than to 

 allow dust and soot, crumbling putty from laps, and 

 mortar out of brick walls, to foul the glass, and 

 shut out solar light from plants that have been ac- 

 customed to double, treble, or even ten times as 

 much of it in a state of nature as it is possible to 

 provide for them in our climate, do what we may. 



Deep and dirty laps, again, are a most preposterous 

 contrivance to make glass roofs opaque. What with 

 the actual width varying at times from a quarter of 

 an inch to an inch, and the residuum that flows from 

 and stains the bottoms of these collectors and dis- 

 tributors of pollution, a third of the glass is not 

 unfrequently obscured by laps. 



The tendency of all improvements in glazing, as 

 will be gathered from subsequent details, is to reduce 

 the number and contract the size of laps. Still, as 

 they exist now, they are often a great msans of shut- 

 ting out the light and lessening the transparency of 

 glass roofs. 



Bringing the Roofs down Closer to the 

 Plants. — Another method of accentuating as it 

 were the energy of the light, consists in either 

 bringing down the roofs into closer proximity to the 

 plants, or lifting the plants up nearer to the light. 

 Doubtless, were roofs perfectly transparent, the mere 

 matter of distance from the glass would be a matter 

 of little moment ; but as they are, the light appears 

 to lose more force the further it passes througk 

 them. Hence, in practice, and notably among Or- 

 chids, it is found that the nearer in reason the 

 plants can be placed to the glass, the more potential 

 the light in strengthening and maturing growth. 

 Short of contact with the glass — and this is to be con- 

 demned on many grounds — not a few plants thrive 

 best as near to it as possible. Actual touch leads to 

 scalding, freezing, and other evils, but the best place 

 for many stove-plants and Orchids will be found 

 within the distance enclosed within six inches and a 

 yard of the glass. 



Hence, where plants on stages or shelves are the 

 main consideration, few or no climbers should be 

 introduced or trained on the roofs. Few have the 

 courage to suppress beautiful climbers sufficiently to 

 prevent their injuring the plants below them by 

 their shade, and hence it is better not to plant, or 

 to confine them to the front, back, and side walls, 

 or roof -pillars. In many cases, however, a roof 

 wreathed and festooned with climbers is far more 

 beautiful than any or all the jplants grown in pots 

 or planted out in beds in the centre or sides of the 

 house. But such climbers inevitably injure by 

 their shade most of the other plants, and if dis- 

 appointment is to be avoided, this should be well 

 understood beforehand. Some contend that light is 

 of far less moment than is mostly assumed, and cite 

 in proof the necessity and constant practice of arti- 

 ficial shading. But the shading is not used as against 

 light, but heat. The term shade is quite misleading. 

 They should be called anti-scorchers. We have 

 never enough light for tropical plants in our climate. 

 We may often, in the highly artificial conditions of 



