VII. FORMULA EXPLAINED. 77 
area, so as to separate the true and the false with anything like 
the same care and confidence given to the sifted records of 
localities within our own island. Many errors likely exist in the 
numerous Floras and other writings consulted, without an English- 
man being able to detect and correct all their errors ;—any more, 
for instance, than a Foreigner would be able to see and amend all 
the many errors about plants and their places, which are still to 
be found within our home books on the botany of Britain; and 
which are repeatedly cited by the continental botanists as if they 
were true and unquestioned facts ;—even still so cited and re- 
peated by various English botanists themselves. 
It is also to be kept in recollection, in attempting to trace 
species-distribution over distant lands, that the geographical inves- 
tigation becomes greatly entangled with questions and opinions 
about the technical distinctness of the plant-species themselves ; 
with questions as to what foreign forms ought to be united 
with, or to be kept separated from, the special forms known in 
Britain, or in Britain and Europe. This is the case, for example, 
with various East-Asian and American plants; their position 
under the names of European species depending upon the indi- 
vidual opinions of botanists; some holding them entitled to dis- 
tinctive names, as species ; others placing them as varieties under 
single specific names. Theories about centres of distribution, 
about migrations and modifications of species, also inconveniently 
interfere with good judgment. Such theories cause alleged facts 
to be recorded in a misleading manner, or to be so tabulated as to 
become unavailable for any use beyond the one purpose of making 
out a seeming evidence in support of some foregone conclusion or 
fanciful hypothesis ; perhaps only such an one as would imme- 
diately fall before a fair and plain record of the simple facts 
themselves. English writers on phyto-geography have sinned 
greatly against a logical philosophy in this wise; almost all of 
them treating their facts unequally and one-sidedly ; the sup- 
pressed portion being just those facts which would alter or modify 
the bearings of the others, if all were fully and fairly given alike. 
Moreover, alleged similarities between plants are sometimes 
