152 DOUBTS ABOUT BOTTOM HEAT. 



An opinion has, nevertheless, been entertained, that bottom 

 heat is useless; there is in the Horticultural Transactions, 

 (vol. iii. 288) a paper to show that it is injurious; and the 

 authority of Mr. Knight has been referred to in support of the 

 opinion, in consequence of that great horticulturist having 

 expressed a belief that the " bark-bed is worse than useless." 

 {Hort. Trans., iv. 73.) But Mr. Knight repeatedly disavowed 

 entertaining any such sentiments. In one place, he stated that 

 the temperature of the air of the stoves in which his Pine-apple 

 and other stove plants grew, without ba/rk or other hot-bed, usually 

 varied from 70° to 85° ; and that the mould in his pots, being 

 surrounded by such air, acquired and retained, as it necessarily 

 must, very near the same aggregate temperature, but subject 

 to less extensive variation {Gard. Mag. , v. S65):m another, he 

 says the temperature of the air was varied in his stove generally 

 from about 70° to 85° of Fahrenheit; and he ascertained, by 

 keeping a thermometer immersed in the mould of the pots, that 

 the temperature of the soil varied very considerably less than 

 that of the air of the stove ; the mould being in the morning 

 generally some degrees warmer than the air of the house, and in 

 the middle of the day, and early part of the evening, some 

 degrees cooler. ( Hort. Trans., vii. 255.) It is, therefore, clear 

 that he considered a high temperature necessary for the roots 

 of his Pine-apple plants ; and we find from one of his papers 

 {Hort. Trans., iv. 544), that he considered it better to obtain the 

 requisite temperature from the atmosphere than from a bark-bed, 

 the usual source of bottom heat, " because its temperature is 

 constantly subject to excess and defect;" and he even admitted 

 that if the bark-bed could be made to give a steady temperature 

 of about 10° below that of the day temperature of the air in the 

 stove. Pine plants would thrive better in a compost of that 

 temperature than in a colder. The dispute about bottom heat 

 was not as to the necessity of it, but as to the manner of 

 obtaining it, which, as it concerns the art of gardening, I need 

 not further notice. 



We have, doubtless, much to learn as to the proper manner 

 of applying bottom heat to plants, and as to the amount they 

 will bear under particular circumstances. It is, in particular, 



