THE CONSTRUCTION OF PLANT HOUSES. 89 



plate and the heat will pass off without injury to the plauts. If 

 the ventilation is at the bottom and top of a high house, it acts like 

 a chimney in creating a strong and injurious draft, drying the 

 plants, and passing oft' the cooler air of the house instead of the 

 heated air next to the glass. Without doubt, the system of 

 ventilating apparatus having gear and worm attachment for open- 

 ing the ventilators is the simplest in construction, neatest in 

 appearance, and the least likely to require repairs. It is the only 

 system adapted to all kinds of conservatory work, where a good 

 appearance is an important consideration. 



Glass. — A very fine quality of glass for greenhouse purposes 

 is now made in America. This statement may be a surprise to 

 some who have been in the habit of depending on foreign importa- 

 tions for a superior article, and it is only within a very short time 

 that such a statement would have been true. The use of natural 

 gas and other improved methods in its manufacture, and greater 

 care in selecting the grades have established its equality. The 

 double thick will average nearly ten per cent thicker and stronger 

 than the French glass, and in a hail storm this might easily mean 

 the difference between a broken roof or one that stood the storm. 

 The size of glass to be recommended depends largely on the style 

 of roof to be covered; 12, 14, and 16-inch widths and lengths of 

 from IG to 24 inches embrace the sizes best suited to greenhouse 

 work. The use of obscured or ground glass in conservatories and 

 houses for palms, ferns, and tropical and other foliage plants is 

 generally commended by gardeners and florists who have had 

 experience in growing plants under it. Its advantages are in not 

 drawing or burning the plants, no matter how far they may be 

 placed from it ; it renders the light more soft and genial, the 

 coloring of the flowers and foliage is improved and retained in 

 good condition a much longer time, and the unnatural burning 

 sensation caused by the sun shining through clear glass is 

 effectively removed without perceptibly diminishing the amount of 

 light in the house. 



Glazing. — What is the best method of glazing? is a question 

 which is frequently asked, and in many cases not from mere 

 curiosity but from a very laudable desire to secure something 

 better than the inquirers now have, or, if about to glaze a new 

 house, to do it in the best way. There is nothing in the market at 

 the present time but what has been fully tested and its merits and 



