33° 



BOTANICAL GAZETTE 



[may 



ing a thick and permanent carpet which may be lifted from the rock 

 at its edges, but which is firmly anchored at its point of origin. 



We now come to the group of invaders that is advancing toward 

 the heads of the canons from below. The pioneers arc few in species, 



+ 



but exceedingly numer- 

 ous in individuals, cov- 



ering the areas over which 

 they advance with a thick 

 carpet of vegetation. 

 Their line of attack is 

 along the w^atercourses. 

 It has been said that dep- 

 osition of earthy matter 

 from the melting snows, 



fine rock material, and 

 some organic matter from 

 the plants 



growmg 



m 



cracks farther up, is con- 

 tinually going on where 

 the current of the water- 

 courses slackens. The 

 first plants to appear in 

 this sediment are usually 

 mosses, including Philo- 



notis i 



which 



sometimes becomes es- 

 tablished even in shallow 

 water. The mosses are 

 followed by species 



of 



Fig. 5. — View in Chasm Lake Canon; tlie wet 

 meadow vegetation in the foreground has com- - , 



pletely filled a basin; similar patches of vegetation of their creeping stemS 



Carex, which by means 



are visible in the vicinity of the cascades. spread extensively and 



form thick mats. Grasses now come in, with a scattering of other 

 herbs characteristic of marshy ground and stream banks, nearly all of 

 which are found in marshy situations at considerablv lower altitudes. 

 The deposits of humus from these plants hastens the filling-in of the 



meadow 



