This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Besides keeping the walls and woodwork of glasshouses clean with limewash, paint, etc, it is more or less essential at times to fill the atmosphere with fumes that are deadly to pests that may be actually feeding upon the crops, or are likely to become a nuisance in that way. In former days the only method of cleansing a glass structure was by applying tobacco smoke in some way or another. If the genuine tobacco could not be afforded, rags and paper steeped in tobacco juice were utilized as substitutes. The tobacco, rags, or paper were placed in flower pots, or old saucepans, buckets, etc, with holes in them, on a few live coals in the bottom. The fumigating mixture was damped, but not sodden, with water, to prevent the flaring of the material, which would have been injurious to the plants in that state. By means of bellows the fire was kept alight, and as the moistened tobacco, paper, or rags were consumed, dense volumes of smoke filled the atmosphere, and while it destroyed the pests, if sufficiently powerful, also upset the operator in many instances. Great improvements have taken place in fumigating greenhouses of late years, and fumigating cones of various descriptions are now in use that will fill the house with fumes after being lighted, and will not necessitate the close attention of the gardener.