la ted 
ON APHYLLOSTACIIYS. 223 
a lively interest in Darwin's theory, not even condescend to enter 
into a comparative examination of the fossil plants, and accuse our 
knowledge of them (which he himself has so much advanced) of a high 
degree of imperfection. I take it upon me to appear in their defence, 
and to point oufct|ie principal results which have already been esta- 
blished, and which can by no means be regarded as props of the 
theory of transmutation. 
1. The Orders, families, genera, and species of the fossil flora 
"ere not always equal. Most of them have had a very unequal dura- 
tion, and been subject to violent changes. There are but few instances 
of the extinction of complete Orders, and these are as yet known only 
to occur in the terrestrial flora of the Palaeozoic period, as the Calemtta, 
Anrmlaru*. , Noggerathue, and SigillaruB; but much more common is 
the disappearance of families, as of Calamites, Lepidodendron, or iso- 
"'" J genera, as amongst the Ferns of those founded upon fronds, Odon- 
topteris, Calipleris, and Dictyopteris, and perhaps also of those founded 
upon steins, Asterochlaua, Tulricaulis, Ptychopteris, etc. 
In subsequent geological periods the extinction of whole Orders of 
plants does not take place, scarcely even that of families, although we 
meet with instances in the Bunter Sandstein of the Trias, which im- 
mediately succeeds the Palaeozoic period, if we regard the curious Scld- 
Wmmtb and Mhophyllum as a distinct family, and also the Sigillaria- 
e Pl ™>-omoia, which is, as it were, an echo of that Order. The ■ 
generic type also approaches more and more the existing, and only the 
Coniferous genera Voltzia and Albertia, of the Bunter Sandstein pre- 
serve characters materially differing from those of the present time, 
ubsequent discoveries may possibly set aside these differences, but 
16 ,esu lts just pointed out are too well established to be materially 
< en, even if we should succeed in obtaining further disclosures about 
e nu 'nerous fruits of the Paleozoic formations. 
1 re gnrd to species, we find their duration generally restricted to 
greater geological periods, and only in isolated instances, occurring 
otn the older and newer formations or divisions. An overleap- 
o ot certain formations of the same period, or even whole periods, as 
s ated to be the case with the fossil animals, has as yet not come to 
J nowledge. Prom my own observations I have not found a single 
pant which may with certainty be shown to have passed from the 
er 'nian formation to the Trias. VoVzla htterophylla and Equiselites 
R 2 
the 
