ON GENERA AND SPECIES, 33 
auxilliary characters in the grouping of species, which with 
his published observations above noticed, I, in time, consi- ` 
dered myself competent to publish my views. This I did 
in a treatise entitled “On Arrangement and Definitions of 
the Genera of Ferns,” which was read before the Linnean 
Society in 1840, and afterwards published in Hooker's 
“ Journal of Botany,” in the volumes for 1841 and 1842, 
occupying 131 pages, and accompanied by a plate showing 
the principal forms of venation. In this I characterised 
143 genera, accompanied by examples of a few of the most 
typical species of each genus, and with observations on the 
natural affinities of the genera, Just as my treatise was 
completed, but before its publication, I received Presl’s great 
work “ Tentamen Pteridographew,” and it was gratifying 
to me to find that my views in general coincided with those 
of that celebrated Pteridologist, I, however, differed from 
bim in some important particulars, chiefly with regard to 
the relationship of the genera to one another, consequent 
on the data on which Presl founded his tribes, placing 
naturally allied species far apart. My endeavour was to 
associate the species possessing the same general features 
in respect to their modes of growth (habit), so as to form 
natural sequences of genera, This I have endeavoured to 
complete by drawing up a general arrangement, which 
forms the second part of this volume. 
The following is an abstract of my arrangement in 
184] .— 
Division I. —POLYPODIACELE, R. Br. 
| Sporangia furnished with a vertical ring. 
Tribe 1.—Potypopisa, J. Sm. 
Sori punctiform, oblong or linear, naked or included 
under the universal indusium. 
Sect. 1. Orthophlebiew, J. Sm. Veins free. 
