38 OUTLINES OF FORESTRY. 



to exist there naturally. If interfered with, to 

 even a comparatively trifling degree, such changes 

 may be produced in the soil, climate, or other 

 conditions as will bring wide-spread destruction 

 to widely separated sections of the country. 



Speaking of the vitality of seeds, Marsh, in his 

 work entitled " The Earth as Modified by Human 

 Action," * page 295, says : 



" When newly-cleared ground is burnt over in the United 

 States, the ashes are hardly cold before they are covered with 

 a crop of fire-weed, Senecio hieracifolius, a tall, herbaceous 

 plant, very seldom seen growing under other circumstances, 

 and often not to be found for a distance of many miles from 

 the clearing. Its seeds, whether the fruit of an ancient vegeta- 

 tion or newly sown by winds or birds, require either a quicken- 

 ing by a heat which raises to a high point the temperature of 

 the stratum where they lie buried, or a special pabulum fur- 

 nished only by the combustion of the vegetable remains that 

 cover the ground in the woods. 



"Earth brought up from wells or other excavations soon 

 produces a harvest of plants often very unlike those of local 

 flora, and Hay den informs us that on our great Western desert 

 plains, wherever the earth is broken up, the wild sunflower 

 (Helianthus) and others of the taller-growing plants, though 



* Reprinted, by permission, from " The Earth as Modified by 

 Human Action," by George P. Marsh. New York : Scribner, 

 Armstrong & Co., No. 654 Broadway, 1874. Pp. 656. 



