D10ECIA. 17 



LEAST WILLOW, Sallv herlacea. This is 

 the least of all trees ; the stems of which, though 

 scarcely two inches high, are truly woody and peren- 

 nial. The woody roots are of a greater extent, creep- 

 ing and running deep into the rocky soil which this 

 species inhabits, about the tops of the highest moun- 

 tains in Scotland, Wales, and Cumberland. It has 

 been gathered on Ben Lomond. 



This Genus has not yet been well investigated ; at 

 present there are enumerated fifty-three species, of 

 which forty-five are English 5 and this is the only 

 British Genus of this Order. These plants are very 

 easily propagated, and remarkably tenaceous of life; 

 hence they have been often used in experiments to 

 ascertain some principles in vegetable ceconomy. 

 Van Helmont, a celebrated physician and chemist, 

 planted a willow, (the species is not defined) weigh- 

 ing fifty pounds, in a certain quantity of earth covered 

 carefully with a sheet of lead : he kept it in this state 

 for five years, watering it with distilled water; and at 

 the end of that time the tree weighed 169 lbs. 3 oz. 

 The earth in which it had vegetated, being weighed 

 at the same time, was found to have lost no more 

 than three ounces. Boyle repeated the same experi- 

 ment upon a plant, which at the end of two years had 

 gained fourteen pounds without the earth in which it 

 had vegetated having lost any perceptible portion of its 

 weight. These facts serve to shew how very impor- 

 tant air ard water are to the increase of vegetation; 

 but by what law of nature these elements are con- 



VOL. III. B 



