sts to an
agreement how to rank doubtful forms. Yet it must be confessed, that it
is in the best-known countries that we find the greatest number of forms
of doubtful value. I have been struck with the fact, that if any animal
or plant in a state of nature be highly useful to man, or from any cause
closely attract his attention, varieties of it will almost universally
be found recorded. These varieties, moreover, will be often ranked by
some authors as species. Look at the common oak, how closely it has
been studied; yet a German author makes more than a dozen species out
of forms, which are very generally considered as varieties; and in
this country the highest botanical authorities and practical men can be
quoted 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 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 will rise to a climax.

Certainly no clear line of demarcation has as yet b