CHAP. I.] CRASSULACEiE. 365 



ORDER XC— PARONYCHIEiE. 



Weedy plants, containing among other ge- 

 nera, Knot-grass {Illecebrum), and Strap wort 

 {Corricjiola). The new order Scleranthacese 

 has been separated from this ; and it takes its 

 name from the British weed, Knawel (Scleran- 

 thiis) . 



ORDER XCL— CRASSULACEiE.— THE HOUSELEEK 

 TRIBE. 



The common Houseleek (Sempervivum tecto- 

 rum) grows, as is well kno\\Ti, on the tiles of 

 houses, or on walls, where there does not appear 

 a single particle of earth to nourish its roots. 

 The leaves are, however, so contrived as to 

 form a cluster of flat scaly circles, and thus to 

 shade and keep moist the roots beneath them. 

 The flowers, which are produced on a tall 

 flower-steiii rising from the leaves, are pink, 

 and usually consist of a green calyx, cut into 

 twelve segments, and a corolla of twelve petals, 

 with twelve stamens and twelve carpels, which 

 spread out like a star in the middle of the 

 flower. The number of petals, &c., is by no 

 means constant, as it varies from six to twenty ; 

 but the other parts of the flower vary in the 

 same manner, and always agree with each other. 



