S74 Dr 071 Antediluvian Plants. 
in others, from which the carbonaceous bark has been removed, 
impressed or elevated dots spirally disposed around the stem, in 
the same manner as the scales. 
I have now finished my observations with regard to the mo- 
nocotyledonoiis genera of antediluvian plants ; but there remain 
certain other forms, the structure of which so far differs from that 
of the above^ as to render it necessary to call in the aid of dico- 
tyledonous plants for their determination. There exist in our 
coal-mines sufficiently numerous examples of petrified^ forms, 
frequently several feet long, remarkable for tubercles or polygo- 
nal impressions distinct from each other, and longitudinally dis- 
posed in straight lines, separated by parallel grooves or ridges, 
and marked with a simple cicatrix impressed in the specimen it- 
self, upon the carbonaceous bark, but elevated in the impression 
or cast. A species of this kind has been figured by Sternberg:, 
PI. 9. f. 1.5 under the name of Lepidodendron alveolatum ; an- 
other by Schlotheim, PI. 19., under the name of Palmacites ocu- 
lotus ; a third, more remarkable for its size, by Nau, PL 4., 
who first referred these vegetables to the Cacti, on comparing, 
at my instigation, several species of our garden. The same 
opinion has been embraced by Rhode^ who, however, seems to 
have gone farther than he was warranted, in consid<ering many 
remains of vegetables as Cacti, which belong to different orders ; 
for some of his specimens are, without doubt, to be referred to 
arborescent ferns. But various kinds of Cacti have been so al- 
tered while involved in the general ruin, as to be in a great mea- 
sure unfit for investigation. We have, for instance, some species, 
such as Cactus tetragonus, pentagonus. liexagonus, which are 
furnished with broad and plane surfaces ; others, as C. cylindrl^ 
cus, entirely cylindrical, and furnished over their whole surface 
with reticulate furrows, among which tubercles project ; others, as 
C. repandus, whose obtuse and repand surfaces are much approxi- 
mated; and, lastly, others, such as all the Opuntice, remarkable for 
their cbm pressed joints, which are plane or sparsely tiiberculate. 
These different forms, then, while they lay buried among stones 
feind mod, have been changed in various ways. A great many 
have been reduced by the extreme prejssure into broad flat" la- 
minae, longitudinally canaliculate or.areolate ; a few have pre- 
