d to show that the
sessile and pedunculated oaks are either good and distinct species or mere
varieties.

When a young naturalist commences the study of a group of organisms quite
unknown to him, he is at first much perplexed to determine what differences
to consider as specific, and what as varieties; for he knows nothing of the
amount and kind of variation to which the group is subject; and this shows,
at least, how very generally there is some variation. But if he confine his
attention to one class within one country, he will soon make up his mind
how to rank most of the doubtful forms. His {51} general tendency will be
to make many species, for he will become impressed, just like the pigeon or
poultry fancier before alluded to, with the amount of difference in the
forms which he is continually studying; and he has little general knowledge
of analogical variation in other groups and in other countries, by which to
correct his first impressions. As he extends the range of his observations,
he will meet with more cases of difficulty; for he will encounter a greater
number of closely-allied forms. But if his observations be widely extended,
he will in the end generally be enabled to make up his own mind which to
call varieties and which species; but he will succeed in this at the
expense of admitting much variation,--and the truth of this admission will
often be disputed by other naturalists. When, moreover, he comes to study
allied forms brought from countries not now continuous, in which case he
can hardly hope to find the intermediate links between his doubtful forms,
he will have to trust almost entirely to analogy, and his difficulties rise
to a climax.

Certainly no clear line of demarcation has as yet been drawn between
species and sub-species--that is, the forms which in the opinion of some
naturalists come very near to, but do not quite arrive at the rank of
species; or, again, between sub-species and well-marked varieties, or
between lesser varieties and individual differences. These differences
blend into each other in an insensible series; and a series impresses the
mind with the idea of an actual passage.

Hence I look at individual differences, though of small interest to the
systematist, as of high importance for us, as being the first step towards
such slight varieties as are barely thought worth recording in works on
natural history. And I look at varieties which are in any degree more
distinct and pe