DISPERSAL BY WIND. 



821 



as their habitat narrow ledges in rocky places, it is inevitable that some of the 

 separated rosettes should fall over the steep wall, and should not come to rest 

 till they have travelled a considerable distance from the mother-plant. Roots are 

 soon developed from the base of the detached rosettes, by which they become fixed 

 to the substratum. Usually a parent plant produces 2-3 rosettes, but frequently as 

 many as six, and the neighbourhood of the terraces overgrown with the species 

 of House -leek figured, and with other allied species {Seinpervivwni arenarium. 



Fig. ibS.—Sempervivum soboliferum. On the lower step of the rock lie five ball-shaped offshoots which have become detached 

 from the upper rooky platform and have rolled down. The butterfly and snail are introduced into the picture to show 

 the true proportions of the offshoots. 



8. Neilreichii, S. hirtum) often looks as if it had been sown with the ball-like 

 rosettes, which have rolled down. 



Sedum dasyphyllum ( see fig. 454 ^ ), which grows in rocky crevices and in the 

 niches of old stone walls, develops offshoots partly in the floral and partly in the 

 foliage region. In the floral region the offshoots originate by the metamorphosis of 

 floral-leaves into foliage. Instead of flowers there are small rosettes (fig. 454^) of 

 thick, ovate, green scales, like those which take the place of flowers in Saxifraga 

 nivalis and S. cerniia (cf. p. 455). These rosettes in the autumn break away from 

 the flower-stalks, and behave just like those of Sempervivum. In the foliage region 

 the oflfshoots arise in three ways. In the axils of the uppermost leaves there is 

 formed a bud which is hardly perceptible to the naked eye. It is embedded in the 



