32 
largely into the composition of coal is certain, from the 
abundance in which its remains occur in particular portions 
of every coal field in Europe and America; and that they 
were the giants of the primitive flora is also evident, from 
their greatly exceeding all other fossil plants in dimensions, 
specimens having been measured by my old friend, R. C. 
Taylor, Esq., in America, upwards of seventy feet in length. 
I have already mentioned the possibility that they might 
have constituted the stems of some of the larger ferns, 
not, however, for a moment confounding them with Tree 
ferns, (Caulopteris) though such was the opinion of Stern- 
berg, and is still so of Brongniart, which theory has been 
ably criticised by Professor Lindley, who considers their 
true affinity as altogether doubtful at present, while Von 
Martius believes them to represent gigantic Cacti, Artis 
placed them with Euphorbiacese, and Schlotheim with Palms. 
Upon this diversity of opinion Dr. Hooker very judiciously 
remarks, " The necessary conclusion to which those who 
place them in the two orders, Cacti and Euphorbiacea?, 
would lead us is, that they were inhabitants of singularly 
arid and desert countries, whilst, if Ferns, they are char- 
acteristic of diametrically opposite conditions, — a moist and 
humid atmosphere." Now the probability is much in 
favour of the latter, as the most conducive to the growth 
and rapid development of a profuse vegetation, such as we 
have indubitable proof existed at the carboniferous epoch. 
The same obscurity which hangs over the real nature of 
Sigillaria extends also to the legitimacy of the species, of 
6. Halonia. — Stem not furrowed, branched, covered with indistinct rhomboidal 
marks and tubercular projections. 
7. Knorria. — Stem not furrowed, branched, marked with projecting scars of 
petioles disposed spirally. 
8. Lepidodendron. — Not furrowed, branched, covered with lozenge-shaped 
scars in quincuncial order, each having a papilla in the upper part, the upper 
portion of the stem and branches with simple linear leaves, the lower portion 
destitute of leaves. 
