A. Gray—Pertinacity and Predominance of Weeds. 167 
plexicaule, which also cross-fertilizes freely. 
n California the prevalent weeds are largely different from 
mostly of indigenous species or immigrants from South 
America; yet the common weeds of the Old World, especially 
of Southern Europe, are coming in. The well-established and 
aggressive ones, such as Brassica nigra, Silene Galliea, Hrodium 
cicutarium, Malva borealis, Medicago denivculata, Marrubium vul- 
gare and Avena sterilis, were perbaps introduced by way of 
Western South America. They are mostly plants capable of 
self-fertilization, but also with adaptations (of dichogamy and 
otherwise) which must secure occasional crossing. 
We cannot avoid the conclusion that self-fertilization is 
A cursory examination brings us to a similar conclusion as 
respects the indigenous weeds of the Atlantic States, those 
herbs which under new conditions, have propagated most 
abundantly and rapidly, and competed most successfully in — 
the strife for the possession of fields that have taken the 
place of forest. The most aggressive of these in the Northern 
Asters and Golden-rods, all insect-visited and dichogamous, 
and Verbena hastata, urticafolia, etc., the frequent natural hybrid- 
ization of which testifies to habitual intercrossing. 
pose that only conspicuous 0 odorous flowers 
ul how bees throng the 
blossoms of Ampelopsis or 
