100 



CASSELL'S POPULAE GARDENING. 



wall-plate on whicli the roof-lights rest in front. 

 The hack walls are built hollow or flued, and the 

 ispent products of combustion are carried through 

 or along the latter. Thus the front walls are im- 

 pregnable to cold, and the back becomes an active 

 and potent source of heat. 



Some of the finest Cattle^^as and other Orchids 

 eyer seen by the writer, and a party of specialists 

 in Orchid-culture, were growing on a shelf along 

 the front of such a sunk house. They were perfect 

 pictures of healthy vigour and verdure, so much so 

 as to excite special admiration and commendation. 

 The house was so simple in its construction, and 

 withal so cheap, that for a time it obtained no credit. 

 But at last the cultivator declared the moist warm 

 wall had very much to do with it, an opinion that 

 all ultimately endorsed. Here was a house little 

 better than a cold-pit, with a path and side shelves 

 all round it, and a bed in the centre, with a faultless 

 collection of Orchids ! Just such a house as any 

 amateur might build for himself, or have erected for 

 him at the smallest cost. The position was specially 

 warm and sheltered, open to the south, and protected 

 by a shrubbery from all winds from other quarters. 

 And the house being so low, it was covered with 

 straw mats on severe nights. By these extraneous 

 aids, and effective means of conserving heat, but 

 little fire-heat was needed, and the results were, as 

 already observed, strikingly successful. 



Nor is the saving of fuel the chief, nor perhaps 

 the most important saving in such cases. The 

 reduction of the amount of heat is often of 

 more moment. The plants are better without so 

 much artificial heat, even if it could be had for 

 nothing. No more mischievous fallacy was ever 

 uttered than that heat is heat, and that all heat is 

 alike good, whatever its source. This is just about 

 the opposite of the truth ; and it would be equally or 

 more true to afiirm that all artificial heat was but a 

 necessary evil, and the less of it used the better for 

 the plants. It is not only difiierent, but inferior to 

 natural heat, its effects on vegetable life and growth 

 being widely different. Hence a degree of natural 

 heat, husbanded or saved, by improved form or 

 structure of plant-stoves and Orchid-houses, or more 

 perfect glazing, or more efficient shelter above or 

 below, is not only a degree gained, but equivalent 

 in growing force, and strengthening transforming 

 power, to two or more degrees. Hence the husband- 

 ing of natural heat is to be strenuously advocated, 

 not only on the ground of economy, but as an aid to 

 culture and a source of strength. 



Importance of Mating Light with Heat. 



— Heat without light stimulates plants into weak- 

 ness. It is most essential to have this in view in 



the culture of stove-plants and tropical Orchids. 

 The preservation of these in health, their successful 

 cultivation, demands a high temperature. Until, 

 however, we can match the heat with the electric 

 light, which seems almost identical with solar light, 

 it is needful to moderate the amount of heat used, 

 so as to make it run more nearly abreast, as it 

 were, with the supplies of light. The exact structural 

 form of house best adapted for husbanding to the full 

 the natural and artificial heat applied, as well as 

 utilising to the uttermost the light of oui- climate, 

 has probably yet to be devised. Nearly a century 

 ago an ingenious horticulturist designed a tropical 

 house that revolved on its base, and presented the 

 best absorbing angle to the sun at every hour thi'ough- 

 out the day. The experiment was so far successful ; 

 but of course the expense proved prohibitory of 

 others on a larger scale, and it is merely mentioned 

 here as an illustration of the thought and care 

 devoted to the ^dtal matter of utilising natural 

 light to the very uttermost. The latter is in fact 

 the difficulty of cultivators. Their cry, like that of 

 the dying Goethe, is " Light, more light ! " Heat of 

 some sort is quite within their control, but light 

 is a sadly limited quantity, and of very mixed 

 quality in our climate. Hence the importance of 

 selecting houses of the best form for conducting light, 

 and for offering as little resistance to its passage as 

 possible, by reason of the opacity of their frame- 

 work, as is consistent with the requisite strength ; 

 choosing glass of the best and most transparent 

 quality, and placing the plants as near to it as is 

 consistent with safety. 



Light Framework.— Whatever the system of 

 glazing adopted, of those to be hereafter described, 

 some sort of strong and durable framework is need- 

 ful. The stronger the material used, the lighter 

 the ribs may be. The desire to reduce the. opacity 

 of rafters and sash-bars to the uttennost, led to 

 the adoption of metallic roofs; and there is no 

 doubt that metal occupies far less space than 

 wood. It is also very generally used, though the 

 idea so prevalent on its first introduction that it 

 would supersede wood for hot-house building has 

 long been laid aside. Hot-houses increase so rapidly 

 that there is abundant scope for both wood and 

 metal in the erection of the framework of their roof. 

 The lightness of metal is undoubted ; but it has 

 many other drawbacks, such as its tendency to cor- 

 rosion, its expansion and contraction under sudden 

 alternations of temperature, and the prejudice against 

 it of being colder than wood. For these and other 

 reasons wood is still very extensively employed, and 

 as the laws of solid principles of building, and the 

 theory and practice of bracing have become better 



ill 



