AMERICAN 
JOURNAL OF SCIENCE AND ARTS. 
[THIRD SERIES.] 
Art. XXVI.—The Pertinacity and Predominance of Weeds ; by 
Asa GRAY. 
A WEED is defined by the dictionaries to be “ Any useless 
or troublesome plant.” ‘EH 
ent possession of soil used for man’s purposes, irrespective of 
his will; and, in accordance with usage, we may restrict the 
term to herbs. This excludes predominant indigenous plants 
occupying ground in a state oF nature. Such become weeds 
when the i ly intrude into cultivated fields, meadows, 
pastures, or the ground around dwellings. Many are unat- 
tractive, but not a few are ornamental; many are injurious, 
but some are truly useful. White Clover is an instance of the 
latter. Bur Clover (Medicago denticulata) is in California very 
valuable as food for cattle and sheep, and sir Pg Cece by 
€ damage which the burs cause to wool. the United 
States, and perhaps in most parts of the world, a large majority 
of the weeds are introduced plants, brought into the country 
Am. Jour. ee panies, Vou. XVIIL—No. 105, Szpr., 1879. 
