Glass is the best agent employed by the gardener to exclude the cold, whilst the light is admitted to his plants which are natives of hotter climates than that in which he cultivates them. Now that the excise-duty is removed from glass, the gardener is enabled to employ the best, and a thicker kind than formerly, when the duty was high in proportion to the good quality and weight. Anxiety to obtain the best glass for hot-houses, etc, is every way laudable; but the benefit sought for is frustrated if it be not constantly well cleansed. The best glass, if dirty, allows fewer rays of light to pass through than inferior glass kept bright. A thorough cleansing should be given both to the outside and inside twice annually, during the first weeks of February and of October, and a third cleansing, on the outside only, at the end of June. In proportion to the deficiency of light does the plant under glass become, in the gardener's phraseology, drawn; that is, its surface of leaves becomes unnaturally extended, in the vain effort to have a sufficient elaboration of the sap effected by means of a large surface exposed to a diminished light, for which a lees surface would have been sufficient if the light were more intense.

The plant with this enlarged surface of leaves becomes unfruitful, the sap being expended in their production which should have been appropriated to the formation of fruit.