GLASS STEUCTURES AND APPLIANCES. 



226 



experience, that the. steeper the angle of the roof the 

 more light passes through it. Hence angles ranging 

 from thirty to forty-five degrees are mostly chosen 

 for early- Vineries, Peach-houses, and other forcing- 

 houses. As pits frequently require additional cover- 

 ing over the glass, and these become very difficult to 

 apply or keep on very steep roofs, forcing-pits with 

 a slope ranging from twenty-five to thirty-five de- 

 grees are often used, and are found to answer well. 



Angle and aspect sire of small moment in the 

 forcing of bulhs and such plants as those already in- 

 dicated. Heat and moisture develop the flowers of 

 such even in the dark, and any excess of light seems 

 to lower rather than foster such growths. But the 

 case is widely different 

 with what may be called 

 the forcing of superior 

 plants, and hence good 

 prepsiration must be made 

 for the application of arti- 

 ficial heat when needed, 

 and for the full utilisation 

 of the light and warmth 

 of the sun, by the use of 

 clear glsiss at a sharp 

 angle, and the placing of 

 it fuU south. More light, 

 and also a larger amount 

 of sun-heat, may often be 

 secured in forcing-pits by 

 altering their form from 

 that of lean-to, to hip, 

 quarter, or full-span pits. 

 Lean-to pits .are with- 

 out doubt the warmest. The back wall proves a 

 good absorber and a fine retainer of heat, and being 

 placed where it cannot escape being heated, it re- 

 turns its heat freely into the atmosphere when it 

 is most needed. The hip-span pit has a small por- 

 tion of the roof formed into a span at the top. 

 The quarter-span has a quarter as much roof at 

 back as at front, whereas in the regular span the 

 two sides are alike. Any of these forms admit more 

 light to the pit than the common lean-to pit, which 

 is perhaps, on the whole, the warmest and the best 

 for forcing. 



The Propagating-pit. — This may, as a rule, 

 be lower and have a flatter roof than the forcing- 

 pit. Free light is wanted, undoubtedly, but almost 

 the less sun-heat the better.. Among the first con- 

 ditions of successful propagation (as will be more 

 fully shown in special articles) is that the heat 

 shall be regular and under complete control ; for 

 few things are more disastrous to the safe and 

 sueedy rooting of cuttings than heat by fits and 

 39 



starts. Valuable beyond everything as solar heat is 

 to horticulture, it is somewhat erratic and wilful in 

 our climate. Now it bursts forth with a fierceness 

 sufficient to wither up all parts of plants into a 

 crippled condition, such as are cuttings at the best ; 

 and, again, it is withdrawn for hours, days, weeks, 

 it may be months. Hence the roof of Uie propa- 

 gating-pit had better be so flat as to be Kttle in- 

 fluenced by the sunshine. A northern or eastern 

 aspect is also quite as good or better for it than a 

 southern one. The light of ttie sun should be wel- 

 comed; its heat cannot be trusted to root difficult 

 cuttings with safety. Such a pit as that shown in 

 Fig. 17 is admirably adapted for propagation. 



Piue-pits, on the con- 

 trary, should be so con- 

 structed as to receive all 

 the sunlight possible to 

 our climate in winter. 

 This plant of the light, 

 heat, and moisture-loving 

 tropics can ill endure the 

 fog and darkness of our 

 wintry skies. Hence the 

 best glass, a considerable 

 pitch, and a southern 

 aspect should be chosen 

 for Pine-pits. The Piue- 

 plant also grows tall, 

 some of them, such as 

 the Providence, running 

 up to four or five feet, and 

 good Queens to a yard or 

 more. Hence Pine-pits 

 should be deep and roomy. Some of the older ones 

 were nine or ten feet wide, and seven feet to ten in 

 depth. Those were the days when hot dung, tan, and 

 leaves in bulk were trusted to as the great sources of 

 bottom and top heat. Considerable masses of these 

 were needed to maintain temperatures of 55° to 75° 

 in pits, with the external air at zero. Pine-pits are 

 less relied upon and important than they were. 

 Some now fruit their Pine-plants in pits, and pits 

 and houses alike are now generally warmed by 

 hot water. Still, there are yet good Pine-growers 

 who do grow a considerable proportion of their 

 succession plants in pits and in fermenting ma- 

 terials. Hence one or more Pine-pits exist in most 

 gardens where Pines are grown, and some of the 

 finest Pine-apples that have yet been produced in 

 this coimtry have been grown in common dung-pits. 

 Boots and top alike enjoy the genial warmth and 

 the nourishing forces evolved from decomposing 

 materials such as horse-dung. Oak-leaves, spent tan. 

 These prove food as well as heat to them. They 

 may be said to be medicine as well, for it is seldom 



Fig. 17. — Spas-boofed Propagating-pit. 

 , Central path ; b, pluugis^-bed, over c, hot-air chamber. 



