LETTER XXXVI. 



THE HOUSELEEK TRIBE PURIFICATION OF THE AIR 



BY PLANTS THE SAXIFRAGE TRIBE. 



Plate XXXVII. 



Hoiiseleek (Sempervivum tectorum) is a very com- 

 mon plant upon the roofs of cottages, and on old walls 

 in the country. Its fleshy, starry leaves, are cooling 

 and juicy ; and, hence, the peasantry employ them as 

 an application upon burns, or in other cases where the 

 skin is inflamed. It is one of those species which are 

 capable of growing in the most dry and exposed situa- 

 tions, often attracting its food from the atmosphere 

 much more than from the scanty source that its roots 

 have access to. It is usually planted by being enclosed 

 in a lump of moist clay, which is stuck upon the naked 

 tiles of a cottage. In such a situation, the young 

 plant first secures itself by putting forth a few roots 

 into the clay, and then gives birth to a number of little 

 starry clusters of leaves, which surround their parent, 

 and overshadow the place where the roots are to conti- 

 nue to develope : in the first instance, protecting it from 

 the glare of the sun, and afterwards forming, by their 

 decay, a soft vegetable mould, into which other roots 

 may penetrate. 



They are enabled to effect this by the power which 



