154 The Philippine Journal of Science ms 
indispensable does not in the least impair the fact that fitness is 
also indispensable. The student uses his time according to his 
ability, and his fitness for the work of a student becomes effective 
as time passes. 
Now, likewise, in the case of plants, if the plant be without 
fitness, time avails it nothing. Assuming the plant to exist, but 
without fitness to endure and to spread, it stands still for a 
longer or shorter time and finally disappears. The doctrine of 
natural selection and survival is a rational one; but would not 
be so, if it ignored time. The fitness of any plant is merely 
ability to make use of time in which to survive, to spread, and 
eventually to keep or to become adapted to the conditions under 
which succeeding ages find it. There could be no sane doctrine 
of natural selection without consideration of the element of 
time; and the early fight of the idea of natural selection for 
general recognition was forced primarily by the necessity of 
past time for the possibility of the evolution that natural selection 
postulated. 
Now, if we recognize, as I do not see how we can possibly 
escape doing, that the demonstration of a relation between time 
and geographic distribution not only does not impair the doc- 
trine of natural selection, but is rather an indispensable and 
inevitable corollary of the theory of natural selection and a con- 
sideration that must be taken into account in the application 
of the theory of natural selection to the understanding of the 
bionomics of any single plant or structure, I believe there will 
remain nothing in this paper by Doctor Willis that consititutes 
an argument against the doctrine of natural selection or that 
offers anything but an invitation for the investigation of partic- 
ular problems in the application of this doctrine. 
To some of these applications, I will return presently. First, 
however, let us note that the difference in view between Doctor 
Willis and myself lies again in the demand made upon the doc- 
trine of natural selection or, in other words, upon what we mean 
by this doctrine. To me, the proposition is simply that those 
plants survive that can — where, when, and while they can. Their 
presence is obviously necessary before they can begin to survive. 
To Doctor Willis, the doctrine of natural selection is something 
which ought to explain the initial presence of the plants. In 
passage after passage, he recognizes the necessity of fitness for 
ultimate survival, sometimes without reservation, sometimes 
with decided qualification for another element classified as 
chance; thus (p. 341) : 
