GREENHOUSE. 



144 



GREENHOUSE, 



materials have been equally spread 

 over the walk. If, however, neither 

 sand nor ferruginous clay can be 

 easily procured, burnt common clay 

 powdered may be mixed with the 

 gravel ; the clay having been burnt 

 by spreading it on the furnace 

 of a hothouse, or by mixing it 

 with faggots, and then setting 

 fire to the whole ; but in this case 

 also, care must be taken that the 

 mixed clay and gravel are watered 

 after they are laid down, and rolled 

 immediately after. 



There are various substitutes for 

 gravel. ''iVhere colour is the object, 

 as well as firmness and smoothness, 

 there is nothing better than burnt 

 lumps of clay, reduced to a very 

 coarse powder, and slightly mixed 

 with Roman cement. Where colour 

 can be dispensed with, a most 

 effective garden-walk, and one which 

 will last for many years, may be 

 formed of the scrapings of public 

 roads, which have been made, or 

 metalled, as road-makers term it, 

 with granite, or other coarse stone, 

 mixed with tar, laid down to the 

 depth of six inches on a bottom of 

 broken stone, and smoothly and 

 firmly rolled. The different kinds 

 of asphalte so laid down also make 

 smooth and durable walks ; but 

 they are too expensive for general 

 use. "When no gravel can be pro- 

 cured, granite or other stone, broken 

 very small, and firmly rolled, will 

 make a very durable walk, though 

 the colour is far inferior to that of 

 fine yellow gravel. For laying out 

 walks, and the mode of preparing 

 the foimdation of gravel walks, &c., 

 see Walks. 



Greek Valerian. — See Pole- 

 mo'nium. 



Green-fly. — See A'phis. 



Greenhouse. — A sti-ucture for 

 growing those plants in (more parti- 

 cularly in the winter season), which 



I will not endure the open air of 

 ! British winters. It may be of any 

 j form, but the most convenient is a 

 i square or a parallelogram, with 

 I upright glass in front, sufficiently 

 I high to admit of walking upright 

 ' under it immediately within the 

 I glass ; and with a sloping roof, at 

 I such an angle as readily to throw 

 off the rain. This roof, for the 



■ better receiving the sun's rays, 

 should face the south, south-east, or 



■ south-west ; and this is called the 

 aspect. The front should seldom 

 be lower than seven feet in height, 



j and the height of the back should 

 I be about two-thirds of the width 

 I of the house. The space within is 

 generally laid out so as to have a 

 shelf in front, about two feet high 

 from the ground, and two or three 

 feet in width ; and next there is a 

 I path two or three feet in width ; 

 i the remainder of the floor, fi'om the 

 I edge of the path to the back wall, 

 I being occupied with a series of 

 I shelves rising one above another like 

 I the steps of a staircase, on which 

 • the pots of plants are to be placed. 

 i These shelves may be nine inches or 

 i a foot in width, and the height of one 

 above another may also be nine 

 inches or one foot. The mode by 

 which artificial heat is communi- 

 cated to such a house is by smoke 

 flues, or hot-water pipes. The fire 

 should be at one end, or behind the 

 house, whichever may be most con- 

 venient ; and the principal flue or 

 ! hot-water pipe should be along the 

 front wall, under the shelf ; or, in 

 some cases, it may be under the 

 path. The reason for this position 

 of the flue or pipe is, that heat 

 [ always ascends ; and, consequently, 

 if the source of heat were placed 

 under the back of the house, the 

 heat would ascend directly to the 

 roof at the upper angle of the house, 

 I and would scarcely heat the lower 



