21 



the roof need be very few, being only required to ren- 

 der the others firm. 



Roof. — The framework of this may be of iron or 

 of wood, and the comparative merits of the two mate- 

 rials are thus fairly stated by Dr. Lindley. The ad- 

 vantage of iron roofs for hothouses are, that they are 

 more durable than wood, and allow a far greater 

 quantity of light to pass through them than wooden 

 roofs, the difference being as 7 to 28, or even 30, in 

 favour of iron, and this is a most important property, 

 when we consider that the healthy action of plants is 

 in proportion to the quantity of light which reaches 

 them. The disadvantages of such roofs are, that 

 they rapidly heat, and as quickly cool down. They 

 are therefore liable to sudden changes of temperature, 

 which can only be guarded against by great attention, 

 which is expensive, and by a large consumption of 

 fuel. We should say use iron, if you prefer success 

 and beautiful form, to cost, and can rely upon the 

 attention of your people ; but employ wood, if you 

 are obliged to study economy. (Gard. Chron.) 



Heating. — Flues, for imparting heat to hothouses, 

 are for the most part superseded by either tanks or 

 hot-water pipes ; but where retained, the top should 

 be formed of iron plates, these admitting the heat 

 most readily into the house, and consequently requir- 

 ing a less consumption of fuel. If it be desirable to 

 have a covering for the flues that will retain the heat 



