150 The Philippine Journal of Science 1916 
familiar structures is understood at the present time. Addi- 
tional structures are being interpreted in terms of utility from 
time to time. I can remember when the serrate leaf-margin 
was apparently a good example of a distinctive structure pre- 
sumed to be beyond the reach of selection; but, for the past 
decade, the serrate margin has been understood to be useful 
under particular conditions and to be correlated in usefulness 
with other adaptive structures. 
Doctor Willis continues to preach mutation in his latest paper, 
and I would argue at greater length against the application to 
natural selection of his opinions on mutation, if it were not 
that he has himself presented with striking clearness a con- 
clusion which does away with any necessity of argument on 
the subject. In the Philosophical Transactions (pp. 329, 330) 
he says: 
We have no criterion to go by, by which to affirm that a certain specific 
difference is “small” and another “large.” We have no right to say, 
for example, that if a leaf of one species is simple and of another compound, 
this is a larger difference' than if one is pinnatifid, the other pinnatipartite. 
We have not the least idea whether the changes in internal construction 
of the nucleus necessary to form Jordanian species are in any way different 
from, or smaller or larger than those necessary to give Linnaean species. 
And a little farther along, 
We must simply take account of all definite and hereditary differences, 
whether we consider them large or small. Every one appears to imply a 
mutation, but whether some mutations are large and others small, we 
have no idea, for we do not know in what a mutation really consists. 
It seems to me better to adopt the' hypothesis that any specific difference 
may appear at one step, whether it be large or small. But we may go 
further than this, and claim that even “larger” differences than any we' 
have as yet discussed may also arise at one step. For instance, the 
endemic Coleus elongatus on the top of Ritigala differs so much from all 
other Colei in its equally toothed calyx, and raceme-like inflorescence, as 
well as in other points, that it must probably be regarded as almost, if 
not quite sub-generically distinct. Yet the whole species is confined to the 
summit of this one mountain and exists there as about a dozen individuals, a 
number which can never have been much exceeded, if at all; and it must 
in all reasonable probability have arisen there at one step. 
But even with the formation of a sub-genus the possibilities of single 
mutations do not cease. * * * The distinction between genus and species 
is really more or less artificial, depending upon our ideas as to what are 
large and what are small changes. 
With these ideas, I am in most complete accord. As long ago 
as 1904, 2 I concluded (p. 426) that “Mutations, or discontinuous 
variations, and the most insignificant of individual variations 
J The variations of some California plants. Bot. Gaz. 38 (1904) 401-426. 
