and thus also the fertile soil layers increase, until the more fastidious plants 

 can subsist. The humblest workers, algae, lichens, cacti and mosses, are 

 followed by sedges, dry grasses, herbs and shrubs, or, in the drier and 

 warmer climates, by agaves and yuccas ; then come ferns and other repre- 

 sentatives of the lower vegetation, succulent grasses and herbs gradually 

 covering the soil with a meadow or prairie, the shrubs become more numer- 

 ous, by degrees closing up, shading the ground and overshadowing the 

 grasses and finally the time is ripe for the arborescent flora. Nor does then 

 the forest appear at once in its fullness and variety of form. Single trees, 



FERNS, SCELERAT LAKE, ALGONQUIN PARK. 



Photo by Houghton W. Wilson. 



stragglers or skirmishers in small numbers, and shrub-like, and stunted 

 forms first arrive, gradually increasing in number and improving in form. 

 These, by their shade and by the fall and decay of their foliage and litter, 

 improve the soil for their betters to follow. 



The Aspen is one of these fore-runners, which, thanks to its prolific 

 production of light, feathery seed, readily wafted by the winds over hun- 

 dreds of miles, readily germinating and rapidly growing under exposure to 

 full sunlight, even now in the Adirondacks, the Rocky Mountains and else- 

 where, quickly takes possession of the areas on which man has ruthlessly 

 destroyed all vegetation by fire. This humble, ubiquitous, but otherwise 



