PR a ee La ee ee OER OR Re re 
1878. ] On the Genealogy of Plants. 367 
group of the club-mosses; and 3d, the horse tail group, or Eguise- 
tacee. The first of these groups seems to have come down to us 
from the Carboniferous epoch almost in an unchanged condition, 
trunks of tree-ferns quite similar to those still found growing in 
tropical countries having been exhumed from the coal measures. 
The second group must be made to embrace the ancient Lepido- 
dendron, which flourished so abundantly in that luxuriant age, 
and whose resemblance to both our club-mosses, and to the 
proper Conifers has been so frequently remarked. In this group, 
therefore, there must have been great degeneracy, as of it the 
forests of that period seem to have been chiefly composed, while 
nothing now remains but the low herbaceous and moss-like plants 
that form our Lycopodiacee} To the third group belonged the 
famous Calamites of the coal beds, and these too have dwindled 
into insignificant rushes. 
Such is in fact the fundamental division of the cryptogamic 
series, and is based as well upon differences of internal constitu- 
tion as of external aspect. If we associate these three classes of 
Cryptogams, respectively, with the three orders of the Gymno- 
sperms, Cycadacee, Contfere and Gnetace@, we shall be able to dis- 
cern many remarkable resemblances which, while they may really 
signify nothing, are sufficient at least to suggest an hypothesis. In 
the first group, or that of the true ferns, we have in the existing 
Rhizocarpee, to which our Azolla belongs, and of which the 
genera Salvinia, Marsilia, and Pilularia have been carefully studied, 
an undoubted transition towards the general condition presented 
by the Cycadacee. It is not unfavorable to this theory of transi- 
tion that the existing forms indicating it are small and humble 
plants. The slight differentiation of the sexless spore into the 
Macrospore and microspore could of itself have scarcely given 
the new form a special hold upon its environment, and we may 
almost wonder that this intermediary stage should not have suc- 
cumbed altogether, as all the later ones probably have done. 
But the true pheenogamic or flowering state once. reached, per- 
manence was acquired, and with it the power of attaining a higher 
development. It is remarkable that this differentiation affected 
the reproductive system only, and has left the woody tissue and 
also the foliage of the fern and the Ay to a great extent 
unchanged. 
1 In the Sunda eke Pits is a Lycopod that attains a diameter of six inches and- 
a height of twenty-five fe 
