INTRODUCTION TO CRYPTOGAMIC BOTANY. 81 



mation of species. If two Floras be formed on different princi- 

 ples — wliile in the one the species are accurately limited, and 

 forms which vary only in some subordinate point, and not in 

 essential characters, are grouped under one common name ; in 

 the other, not only every marked variety, but even accidental 

 variation, is elevated to the rank of a species, — it is impossible 

 to form any correct comparison, and this is the more necessary 

 in Cryptogams than elsewhere, because the species have noto- 

 riously such a wide diffusion, and because their technical, though 

 not their essential characters, are so very variable. The great 

 point in all these cases is never to describe from single or 

 imperfect specimens, where there is some form evidently very 

 closely allied. It may not be possible, perhaps, always to avoid 

 error, but a little caution will be most advantageous, both as 

 to one's own individual character as a botanist, and to science 

 in general. And if species are once accurately characterised, 

 there will be far less difficulty than may be imagined as to 

 genera, i Nothing is more vain than to run down botanists as 

 mere makers of species, as though it did not take as much 

 knowledge and tact to limit species well, as to ascertain a few 

 detached microscopical facts without deriving any general 

 views from such study, or ever seeing the relative bearing of 

 such observations. The physiologists of the present day, at 

 least too many who have some name in science, are absolutely 

 doing the very thing which they profess to despise in species- 

 makers. A proposer of bad, ill-defined species is no promoter 

 of science ; still less is the so-called physiologist who draws 

 from isolated half-observed facts, conclusions which the very 

 next observation may entirely destroy. We may regret, 

 indeed, sometimes the over-caution of the prince of physio- 

 logists, but such over-caution is ten thousand fold more 

 praiseworthy, and tends more to the advancement of science, 

 than crude, hasty, and ill-considered theories founded on imper- 

 fect observations, because what it does bring forth is essentially 

 a KTt]fia tg cui, and, even when incomplete, is a sure step- 

 ping stone for the acquirement of some further eminence. 



20. Before entering into a more particular consideration of 

 the different sections into which cryptogamic plants are divi- 



