PERTINACITY AND PREDOMINANCE OF WEEDS. 241 
element of their predominance. Apparently this question 
_ must be answered in the negative. The question is not 
whether they are self-fertilizable. The great majority of 
plants are so, even of those specially adapted for intercross- 
ing. The plants of this list appear to belong to the juste mi- 
liew. Only one (Rumex Acetosella) is completely dicecious ; 
a few are incompletely dicecious or polygamous ; the two spe- 
cies of Plantago are dichogamous to the extent of necessary 
dioicism or monoicism; a large number of the corolline spe- 
cies are either proterandrous or proterogynous, including two 
or three anemophilous species ; and all the Grasses (which 
form the last quarter of the list) are anemophilous and more 
or less dichogamous, and therefore not rarely cross-fertilized. 
Of those which are not anemophilous we notice none which 
are not habitually visited by insects (except perhaps G'napha- 
lium uliginosum), and which therefore are almost as likely to 
be cross-fertilized as close-fertilized ; while in not a few (such 
as the Composite generally and most of the other Gamope- 
tale) the arrangements which favor intercrossing are explicit. 
There is no cleistogamous and therefore necessarily self-fertil- 
ized plant in the list, except Lamium amplexicaule, which 
also cross-fertilizes freely. 
In California the prevalent weeds are largely different from 
those of the Atlantic States, and, as would be expected, are 
mostly of indigenous species or immigrants from South Amer- 
ica; yet the common weeds of the Old World, especially of 
southern Europe, are coming in. The well-established and 
ageressive ones, such as Brassica nigra, Silene Gallica, Ero- 
dium cicutarium, Malva borealis, Medicago denticulata, Mar- 
rubium vulgare, and Avena sterilis, were perhaps introduced 
by way of western South America. They are mostly plants 
capable of self-fertilization, but also with adaptations (of dicho- 
gamy and otherwise) which must secure occasional crossing. 
We cannot avoid the conclusion that self-fertilization is 
neither the cause nor a perceptible cause of the prepotency 
of the European plants which are weeds in North America. 
A cursory examination brings us to a similar conclusion as 
respects the indigenous weeds of the Atlantic States, those 
