Dr Martins on Antediluvian Plants. 275 
served their orbicular form, their dense and fleshy texture ha- 
ving prevented the impletion of their trunks with mud, and their 
subsequent conversion into a stony substance, as we observe to 
have taken place in other vegetables, and especially the arbo- 
rescent ferns. For which reason, it would seem, that round pe- 
trified Cacti have sometimes been taken for Calamites, as may 
be exemplified in the case of Succow^ who, in the Acta Theod. 
Pal. vol. V. pi. 15., has figured a cacti te for a calamite. With 
regard to the surface, in a few specimens the cortical layer it- 
self remains reduced to a state of charcoal, and exhibiting areo- 
lae formed of lanigerous tubercles, such as we see in Pi. 9. fig. 1* 
of Sternberg ; in others, again, and those more numerous, this 
layer is loosened from the internal parts of the plant, and is ag- 
glutinated to the slate-clay, in such a manner that its internal sur- 
face comes into view, of which an example may be seen in Stern- 
herg^s PL 13. f. 2. ; in others, again, the internal substance it- 
self appears converted into stone, and denuded of its. bark. The 
fourth condition in which cactites occur, is when the impression 
of the natural entire surface has been left upon slate-clay ; and 
the fifth, when the surface, previously deprived of the cbi'tical 
layer, has been impressed upon clay or mud ; the latter of whidh 
affords but a very imperfect idea of the nature of plants, as may 
be seen by Succozv's figures, PI. 19. f. 14. and 15., which can- 
not be reduced to any species. Having now stated the circum- 
stances by which the Cactites may be distinguished from other 
petrified plants, I proceed to give their generic character : 
A woody trunli^ simple or articulato-dichotomous, with con- 
tracted entire geniculi, either longitudinally furrowed, with 
straight or waved sulci, which are impressed at the top witb 
polygonal tubercles perpendicularly imposed upon them, or 
smooth (without furrows), with sparse or reticulate tubercles. 
The splecies with which I am acquainted are the following : 
Cactites giganteus. 
Cylindrical ? sulcate, the sulci straight, with somewhat con- 
vex faces, subhexagonal, contiguous areolae, which are ovate 
from the lower angles, being rounded, and the upper contracted^ 
and marked with three cicatrices toward the tip. 
Figured by Succow^ PL 15. 
