ON GENERA AND SPECIES. 5 
subsequent authors; and in consequence of many species 
of Linnens, Swartz, and other early authors, being but 
indifferently described, many being founded on imperfect 
specimens, and nothing but the meagre description left us 
for their identification, It frequently happens that some 
modern author detects or supposes that he has found out 
that the new species of his contemporary is one of the 
Linnean or Swartzian doubtful species, and on his decision 
being confirmed, names long familiar have to be changed. 
Again, by the distribution of trade and private herbarium 
collections, sets of the same specimens fall in the hands of 
different botanists at the same time, and each being eager 
to describe what he considers new, and not, in some in- 
stances, having studied the special families, nevertheless 
does not hesitate to describe new species, or to found new 
‘genera. This being done without inter-communication, 
different names are given to the same plants; when these __ 4 
are collated by the systematist, it often becomes difficult to 
decide which to adopt, thus burdening the science with 
Beer, 
. Under this state of things few Ferns have now less. than 
bene names, many have twenty, thus rendering it in many 
. eases impossible to reconcile one author's views with an- 
= other’s. For instance, the Fern known by the name of 
| Ceratopteris thalictroides has been described by no less than 
. |twelve authors under as many different generic and mg 
- ‘names, 
Bat the point upon which Segen appear ES es 
| differ most, and upon which their only agreement seems to — 
be an agreement to differ, is the definition of genera and ` 
their limits. I say emphatically appear to differ, for in the — 
works of those most at issue the differences are not so — 
much i in the. limita, of tho gronpe 4 themselves. as in ı the 
