lOi LETTER VL[. 



suspended in air. In some leaves they are extremely 

 large and numerous, and such leaves perspire through 

 the breathing-pores in very great quantity, as the 

 Vine ; in others they are so small or so few, as to ad- 

 mit of scarcely any perspiration, as in the Purslane, 

 and in succulent plants in general. It is thought, 

 indeed, that the character of succulence is owing 

 to leaves being unable to get rid of the water ab- 

 sorbed by the roots, and so becoming, as it were, 

 dropsical. 



Attention to this difference in the power of per- 

 spiring in different plants is one of the keys to a 

 knowledge of the right method of cultivating them 

 and it has been applied for years to succulent plants, 

 by keeping them in what is called a dry stove ; that is 

 to say in a hot-house, the air of which is kept dry by 

 refraining from watering the floors or earthen pots in 

 winter. Succulent plants are, when in a state of 

 rapid growth, so imperfectly supplied with the means 

 of perspiring, that they require all the assistance 

 which can be obtained from a dry atmosphere, to be 

 able to part, by the leaves, with the water that is im- 

 pelled into them through their roots ; and conse- 

 quently, if ever, in a rapidly growing state, they are 

 kept in a damp atmosphere, they become dropsical 

 and unhealthy, or soon decay. But in the winter, 

 the little power of perspiration which they possessed 

 in the full vigour of their summer growth is very 

 much diminished, and is in fact reduced to almost 

 nothing. Their roots will nevertheless go on absorb- 

 ino- moisture from the soil as Ion"' as the soil contains 



