414 BOTANICAL GAZETTE [DECEMBER 
home. Since they all produce seed far in excess of what can grow, 
this means that in time the descendants of a variable plant will be 
found in considerable numbers under very different conditions; and 
that in this way it will be able to have many more descendants than 
the non-varying plant, the space available to whose offspring is lim- 
ited. More descendants bear more seed, likewise variable, and with 
that they will thrive wherever they fall. And so the variable plant 
has some advantage in competition with the specialized one even 
where the latter is at home. 
Where the environment is uniform over great areas, then natural © 
selection breeds very close to a type, and considerable variation is 
a disadvantage; but where there are great and constant local differ- 
_ences in environment the premium is taken off of specialization, and 
natural selection favors a relatively high degree of variability. In 
such a place we find not merely that plants vary with the environ- 
ment, but that in any single spot the individuals vary conspicuously 
as well. 
If this is the real explanation of the variability of these plants, it 
is to be anticipated that plants of restricted range and characteristic 
habitat in this same locality will be more specifically adapted to 
their particular habitats, and when growing side by side with the 
ubiquists will be less variable. I have already pointed out that this 
is true among the oaks. The only other Rhamnus of this neighbor- 
hood, R. crocea, is not abundant enough even in spots to prove any” 
thing. In each of the other genera I have used, Arctostaphylos, 
Baccharis, and Ceanothus, we have other species of relatively local 
occurrence and relatively limited variability. 
Baccharis viminea DC. isa plant of local occurrence on the flank 
of the mountains. Its leaves are sometimes entire, at other times 
sparsely serrate toward the apex; otherwise it is very constant. Arc- 
tostaphylos Andersonii Gray grows only near the mountain tops = 
the fog belt. The following measurements are of five plants select 
in the field to show the extremes of variation; twenty-seven plants 
selected as were those of A. tomentosa would probably have varied 
less widely than these five do. No entire leaves were found. 
Shape: 161, 169, 200, 203, 207 
ength: 35.5, 44, 54, 46, 41-9 
Serration %: 18, 29, 39, 29 
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