1904] COPELAND—VARIATION OF CALIFORNIA PLANTS 425 
taken it was certainly as small as can be imagined. And surely there 
is no point between the formation of an extra cotyledon and that of an 
added leaf on a season’s growth where mutations leave off and varia- 
tions begin. Both begin with the formation of two growing points 
from one. Every step in growth is an insensible move from the pre- 
ceding state; and variation, inexorably dependent on growth for its 
appearance, cannot be less continuous than growth is. 
It may be objected to this argument that the variation does not 
occur in growth, but before it begins; say in the formation of the germ 
cells. That cannot be demonstrated, even in as favorable subjects 
as the insects. And if it were really and demonstrably true, it would 
hot damage the argument, but merely shift it. Life is an uninter- 
tupted process from generation to generation. The division of the 
chromosomes, the reduction in their number, and their combination 
in the sexual union are orderly, regular processes, just as the growth 
of any individual is. In Our ignorance of the forces at work and their 
way of working I can imagine no discontinuity in these finer, more 
tecondite processes, any more than in more visible growth. Nor can 
T see why we should regard differences between twin organisms as not 
arising in growth because we suppose their environment to be identical, 
and on that ground refer the differences which we certainly do see to 
still earlier stages in ontogeny, perhaps even antedating fertilization ; 
unless we can show differences in the environment there. It is perhaps 
natural to suppose that the things we do not understand happen in 
the stages we know least about, but this assumption does not share the 
nature of a proof. It is therefore sophistry to plead that variations 
are independent of growth as an objection to the principle that they 
mnust be as continuous as growth is. 
If variation is a phenomenon of growth, it may occur wherever 
growth is going on. In the beginning of this paper I have pointed out 
that it actually does this in the oaks I studied. It is as reasonable to 
Speak of variation localized in the parts of a tree, each the product 
of the activity of an isolated meristem, as to regard the differences 
tween parthenogenetically produced offspring of a single parent as 
“xamples of it. Kxrzxtocc has shown that variation is more consid- 
‘table among the parthenogenetically than the bisexually produced 
members of a hive of bees. 
