INTRODUCTION. 39 



There is another reason for deep trenching", 

 which is no doubt as beneficial to flowers as it 

 is to all other plants ; viz. they receive a greater 

 share of that genial moist warmth which is at 

 all times rising from the interior of the earth to 

 its surface. This is a circumstance not enough 

 attended to; and by many practitioners quite 

 unheeded : it is, nevertheless, a great assistant 

 to vegetation. According as we descend, the 

 temperature increases. In the winter and spring 

 months, it is by several degrees warmer at 

 the depth of three feet than at or near the 

 surface. The ground being opened to that 

 depth, therefore, permits the ascent of this warm 

 steam in cold weather, and allows it to rise like 

 a refreshing vapour when the weather is hot and 

 dry ; in both seasons of much advantage to the 

 roots. 



Friability. — That flowers may have every en- 

 couragement from the constitutional texture of 

 the compost they are placed on, it is prepared by 

 being compounded, aerated, and screened, till it 

 is free from stones, clods, &c. and all of a uniform 



