62 Bibliographical Notice. 
The want of a uniformity of value in the several groups is stated 
to be the bane of the botanical geographer: Orders are unequal, 
Genera unequal; Species are unequal too (p. 44). (Here we are 
tempted to ask, how should we expect mathematical proportions 
where variety is as much the rule as unity is the law?) But 
the species are in the worse predicament, that the little we know 
of their distinctness and limits does not agree with our own defini- 
tion: our conclusions are only inferences from data and proofs 
equally incomplete (p. 28). We much fear that human knowledge 
is doomed to remain imperfect in this particular. Such universal 
experience, extending over a series of years sufficient for such 
proof, is probably not within the reach of man. We commend 
Mr. Watson’s definition of a species (p. 31), and his criticism on the 
subject, to those who wish for a near approach to the desired goal. 
The illustration given (pp. 48 & 279) of three grades of species is 
very apt :— 
1, Rubus fruticosus: a super-species (?supra- Linnean), or 
aggregate. 
2. R. saxatilis: a true species, or integrate. 
3. R. discolor: a sub-species, or segregate (? infra-Linnzan). 
4. Veronica agrestis: a dimidiate species, 7. e. a species halved, 
by the separation from it of V. polita. 
The uncertainty (or want of fixedness) in species, as shown by the 
varying opinions of different authors, and even by the successive 
editions of the same writer, is sufficiently familiar to all those who 
have made a serious study of botany; and if the inconsistencies in 
the practice of authors are very clearly set forth (pp. 40, &c.), it is 
only one more proof of the fallibility of human judgment, and of the 
imperfection of our knowledge. May we hope that the rising genera- 
tion of botanists, whose attention is thus called to a matter of no 
slight importance, will be found ready to double their efforts to re- 
move this imputation of inconsistency by the only means from which 
there is no appeal—by a careful series of experiments and diligent 
cultivation of the plants. 
The permanence of species is another question discussed in this 
chapter ; but as this lies at the very root of Mr. Darwin’s theory, 
we need not do more than refer our readers to the many able 
reviews and discussions which have so recently appeared upon the 
‘Origin of Species.’ 
Chapter III. deals with the “introduced species,’ a subject on 
which no one can be more at home than Mr. Watson; for to him is 
due very much of the progress recently made in this country in distin- 
guishing strictly between such plants as are believed to be aboriginal 
(z. e. prehuman natives of the soil) and those which are either sus- 
pected or proved to have been imported by human agency. 
We cannot help thinking that much yet remains to be done in the 
way of curtailing the given range of many plants—truly native, may 
be, in the south of England, but very unjustly reckoned indigenous 
to the northern counties, Scotland, or Ireland. Nay, there are 
Ce ee a eT 
