PORTABLE, TEMPORARY, AND MOVEABLE STRUCTURES. 135 



between the canvas and the wall is nine inches wide at top, and four 

 feet wide at the bottom, as in the Horticultural Society's garden, the 

 syringing can be very well performed in the space within. 



(A broader coping would be far better. No temporary coping should 

 be less than two feet in diameter, and it should always be inserted 

 beneath a short permanent one. This is by far the best way of pro- 

 tecting fruit-trees, and the coping is so wide that it is seldom anything 

 is required in front of the wall.) 



A very simple and efficient apparatus for rolling up and letting 

 down canvas shades over the roofs of hothouses was brought into use 

 in the kitchen-garden at Syon by Mr. Forrest ; and as it is equally 

 well adapted for covering awnings for tulip-beds or other florists' 

 flowers, and for a variety of other garden purposes, we shall here give 



Fig. 109. 



Apparatus for rolling up and letting down canvas shades. 



such details as will enable any intelligent blacksmith or carpenter to 

 construct the apparatus. The canvas is fixed to a roller of wood, fifty 

 or sixty feet in length, the length depending on the diameter of the 

 pole or rod, fig. 109, a, and the toughness of the timber employed, as 

 well as the dimensions and strength of all the other parts. On one end 

 of this rod, and not on both, as is usual, a ratchet wheel, 6, is fixed, 

 with a plate against it, c, so as to form a pulley-groove, e?, between, to 

 which a cord is fastened ; and about three inches further on the rod is 

 fixed a third iron wheel, about six inches in diameter and half an inch 

 thick, e. This last wheel runs in an iron groove,/, which extends 

 along the end rafter or end wall of the roof to be covered. The canvas 

 or netting being sewed together of a sufficient size to cover the roof, 



