. Cyclopedia of American horticulture, comprising suggestions for cultivation of horticultural plants, descriptions of the species of fruits, vegetables, flowers, and ornamental plants sold in the United States and Canada, together with geographical and biographical sketches. Gardening. GREENHOUSE the thoroughness of the annealing. Glass is annealed by passing through a series of ovens, where it is raised to a high heat and then gradually cooled, whatever toughness and elasticity the finished product may con- tain being due to this pro- cess. The thickness of glass ». "^â *^ varies, not
. Cyclopedia of American horticulture, comprising suggestions for cultivation of horticultural plants, descriptions of the species of fruits, vegetables, flowers, and ornamental plants sold in the United States and Canada, together with geographical and biographical sketches. Gardening. GREENHOUSE the thoroughness of the annealing. Glass is annealed by passing through a series of ovens, where it is raised to a high heat and then gradually cooled, whatever toughness and elasticity the finished product may con- tain being due to this pro- cess. The thickness of glass ». "^â *^ varies, not only with grades - r-,' , , (single and double thick 1. L^ but also more or less within ^Si the grades, and even with ^ different parts of the same '^" pane. Single thick glass is too thin for use in Green- hiMises, and in selecting any L'li 5 for such a purpose it t ';li lie examined pane by , and all showing In I! (I variation in thick- li' . either between panes iir 111 different parts of the , rejected. A pane of varying thickness is much iiiiire liable to breakage from climatic changes or sudden shucks than one which is uniform in this regard. Fnini the foregoing state- iri' iits it will be seen that, in LI , the ordinary dou- li!- Ill irk green glass is best, a, ii-ards both tint and .^llâ ^;u^'th, green <rla'^ i of which is only .iMi ^ h. n |....|, ,,1 ;, ,m , ,i_r,.. The idea has Ion;,' ln-i-n more or li-ss pn-vak-nt that such visible defects in sheet glass as the so-called "bubbles," "blisters" and "stones," produce a focusing of the solar rays passing through them, thus burning the foliage of plants grown under glass containing these defects (Pig. 996). This view has been held by glass manufacturers and horticulturists alike, and seems not to have been publicly contradicted until 1895 (Bull. 95, Cor- nell University Agric. Exp. Sta., p. 278). In view of the erroneousness of this theory, it is r
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