50 
DOUBTFUL SPECIES. 
Chap. II. 
that most careful observer Gartner, they can be crossed 
only with much difficulty. We could hardly wish for 
better evidence of the two forms being specifically dis¬ 
tinct. On the other hand, they are united by many 
intermediate links, and it is very doubtful whether these 
links are hybrids; and there is, as it seems to me, an 
overwhelming amount of experimental evidence, show¬ 
ing that they descend from common parents, and con¬ 
sequently must be ranked as varieties. 
Close investigation, in most cases, will bring naturalists 
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, wiU 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 pedun¬ 
culated 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 wLat 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 
