164 A. Gray—Pertinacity and Predominance of Weeds. 
Europe have to compete with a vegetable world in comparatively 
stable equilibrium of its species, while European weeds coming 
—or which formerly eame—to the United States found the 
course of nature disturbed by man and new-made fields for 
which they could compete with advantage. But his ingenious 
hypothesis is that weeds have a peculiarly “plastic nature, one 
capable of being moulded by and to the new surroundings,” 
by which the plant “ere long adapts itself, if the change is 
not too great or sudden, to its new situation, takes out a new 
lease of life, and continues in the strictest sense a weed ;” “that 
the plants of the European flora possess more of this plasticity, 
are less unyielding in their constitution, can adapt themselves 
oe more oft or aap it succeeds in the New World 
while the less adaptable American flora fails in the i World.” 
So far as we know, the greater plasticity of European as 
bora nes with sites ee plants is purely hypethetcal ‘More 
an h Hearvachs is hardly necessary for the probable bennantion 
of the Aeggreet oy of Old World weeds in the Atlantic 
Dnited 
Mr. Henlow, in his remarkable memoir, On the Self-Fertili- 
zation of Plants (which we reviewed in the June number 0 
this Journal) — from different but equally thooreicel 
premises an opposite Bas seb —namely, that se > } 
intrusive and dominant plants in general, and of grea . 
grating capabilities, ave se a longer an neestral life. ifeears ne 
their less aggressive fekativiens” He also maintains that re 
and oop = ae for domination in the manner of wee 
possess a n characteristic to which this dominance may 
be suribated, ‘ately that they are in general self-fertilized 
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