HOJIE GARDENS FOR SMOKY TOWNS. 285 



drizzle, satisfied me that the mission would fail, even though the 

 sweetbriers were given away by the district visitors ; for these simple 

 hardy plants perish in a mid-London atmosphere unless their leaves 

 are periodically sponged and syringed, to wash away the soot parti- 

 cles that otherwise close their stomata and suffocate the plant. 



It is this deposit that stunts or destroys all our London vegetation, 

 with the exception of those trees which, like the planes, have a de- 

 ciduous bark and cuticle. 



Some simple and inexpensive means of protecting vegetation from 

 London soot are, therefore, most desirable. 



When the Midland Institute commenced its existence in temporary 

 buildings in Cannon Street, Birmingham, in 3854, I was compelled to 

 ventilate my class-rooms by temporary devices, one of which was to 

 throw open the existing windows, and protect the students from the 

 heavy blast of entering air by straining it through a strong gauze-like 

 fabric stretched over the opening. 



After a short time the tammy became useless for its intended pur- 

 pose ; its interstices were choked with a deposit of carbon. On ex- 

 amining this, I found that the black deposit was all on the outside, 

 showing that a nitration of the air had occurred. Even when the 

 tammy was replaced by perforated zinc, puttied into the window 

 frames in the place of glass panes, it was found necessary to fre- 

 quently wash the zinc, in order to keep the perforations open. 



The recollection of this experience suggested that if a gauze-like 

 fabric cheaper and stronger than the tammy can be obtained, and a 

 sort of greenhouse made with this in the place of glass, the problem 

 of converting London back-yards into gardens might be solved. 



After some inquiries and failures in the trial of various cheap fab- 

 rics, I found one that is already to be had, and well adapted to the 

 purpose. It is called " wall canvas," or " scrim," is retailed at 3|c7. 



Eer yard, and is one yard wide. If I am rightly informed, it may be 

 ought in wholesale quantities at about 2d. per square yard i.e., one 

 farthing per square foot. This fabric is made of coarse unbleached 

 thread yarn, very strong and open in structure. The light passes so 

 freely through it, that when hung before a window the loss of light in 

 the room is barely perceptible. When a piece is stretched upon a 

 frame, a printed placard, or even a newspaper, may be read through it. 

 The yarn being loosely spun, fine flutfy filaments stand out and bar 

 the interstices against the passage of even very minute carbonaceous 

 particles. These filaments may be seen by holding it up to the light. 

 The fabric being one yard wide, and of any length required, all 

 that is needed for a roof or side walls is a skeleton made of lines or 

 runs of quartering, at 3 feet distance from each other. The cost of 

 such quartering, made of pitch pine, the best material for outside 

 work, is under one penny per foot run ; of common white deal, about 

 three farthings. Thus the cost of material for a roof, say a lean-to 

 from a wall-top to the side of a house, which would be the most com- 

 monly demanded form, of 30 feet by 10 feet, i.e., 300 square feet, 

 would be 



s. cl. 

 110 feet of quartering (11 lengths) at Id. . ' . . . 92 



300 square feet of canvas, at irf .6 



Nails and tacks, say .10 



* See foot-note, page 293. 10 5 



