Io6 IMPROVEMENTS IN THE CULTURE OF 



of culture I recommend, is as great as that requi- 

 site to raise a forced crop of potatoes. The ex- 

 pense of fuel for my hot-house, which is forty feet 

 long, by twelve wide, is rather less than sevenpence 

 a-dayhere, where I am twelve miles distant from coal- 

 pits : and if I possessed the advantages of a curved 

 iron-roof, such as those erected by Mr. Loudon, 

 at Bayswater, which would prevent the too rapid 

 escape of heated-air in cold weather, I entertain no 

 doubt, that the expense of heating a house forty- 

 five feet long, and ten wide, and capable of hold- 

 ing eighty fruiting Pine plants, exclusive of grapes 

 or other fruits upon the back wall, would not ex- 

 ceed fourpence a day. A roof of properly curved 

 iron bars, appears to me also to present many 

 other advantages : it may be erected at much less 

 cost, it is much more durable, it requires much 

 less expense to paint it, and it admits greatly more 

 light." Hort. Trans, iv. 72. 



Mr. Knight adds, " I have .not yet been trou- 

 bled with insects upon my Pine plants (having 

 only had nine plants for about as many months), 

 and have not, of course, tried any of the published 

 receipts for destroying them. Mr. Baldwin recom- 

 mends the steam of hot fermenting horse-dung : I 

 conclude the destructive agent, in this case, is am- 

 moniacal gas ; which Sir Humphry Davy informed 

 me he had found to be instantly fatal to every 

 species of insect ; and if so, this might be obtain- 

 ed at a small expense, by pouring a solution of 

 crude muriate of ammonia upon quick-lime j the 



