274 On Modern Improvements of Horticulture, 



most necessary accompaniment *,) which may be generated 

 below. 



Light is a most potent agent in the maturation of vegetables : 

 united with a moderate degree of cold^ it is much more effectual 

 in progressive vegetation, than the necessary degree of heat 

 with darkness. Exposure to light is indispensable to plants : 

 and, therefore, our glass cases are formed to admit as much as 

 possible. Within these few years, the endeavour to gain an 

 accession of light by reducing the dimensions of the wooden 

 scantling of hot houses suggested the idea of metallic frames ; 

 and for the concentration of the sun's rays, horizontal as well 

 as vertical curvilinear roofs have been constructed. Lightness 

 to the eye, durabihty, imperceptible expansion, and glazed with 

 panes, cut. like segments of circles, to facilitate the passing off of 

 condensed water, with complete command of ventilation, are an 

 assemblage of properties, always as desirable as necessary ; and 

 as they may be cast in the most elegant forms, and protected 

 by paint, they add greatly to the ornament of the garden. 

 Beautiful as these buildings are, some little disappointment has 

 taken place respecting them : it has been experienced, that 

 the intensity of the sun's light, or heat, has been found detri- 

 mental to the tender inmates, and that shading is as necessary 

 in bright, as light is in cloudy weather. Certain it is, that in the 

 winter season, when light and heat are most desirable, no fear 

 need be entertained from this circumstance ; and it ought to 

 be considered, that in our summer, we have at least, daily, /owr 

 hours more sun than intertropical plants have at home : of 

 course, they have less time for their evening's repose, (which 

 all plants more or less require) ; besides, it should be thought 

 of, that all plants are not equally formed to sustain such a 

 blaze of light ; '' some affect the sun and some the shade ;" 

 such as the pine-apple f, and orange, which require *' a warm 



• The admission of humidity into forcing-houses is attended by the 

 most sakitary consequences : it counteracts the bad effects of fire-heat, 

 and is inimical to many insects. For this purpose, a steam- supplying 

 apparatus is added to the best-constructed hot-houses, productive of the 

 greatest advantages. 



t It has long been observed by gardeners, that the pine-apple always 

 does best in forcing-pits, merely from the circumstance of there being 

 more shade, 



