TA 
376 ; On the Genealogy of Plants. [June, 
may be more clearly presented by means of the following rough 
diagram, in which not only are all additional coôrdinate branches 
left unrepresented, but the continuation of each stage beyond the 
point of divergence is, for the sake of perspicuity, removed, leav- 
ing the differentiations only to stand in naked outline. This dia- 
gram presents the two great lines of descent, that of the Lepi- 
dophytes, of which we have the fossil genus Lepidodendron in the 
Carboniferous, and that of the ferns, trunks of whose arborescent 
forms are also found in the same formation. The line of the 
Equisetaceeé is omitted, although it probably had an independent 
existence, and may yet be found to have a genectic connection 
with some of the higher types. ; 
The order of succession here laid down is confirmed by what. 
is known respecting the time at which each of the several groups 
first appeared in the geological history of the globe. The 
primary divergence must have taken place in the latter part of 
the Devonian age, since within this formation occur some remains 
of Lepidodendron, while fossil trunks both of this and of true 
tree-ferns are found throughout the Carboniferous strata. It was in 
this latter epoch that both the ferns and the Dichotomes or Lycopo- 
dites attained their greatest perfection and abundance. Whether 
any of the large trees belonging to either of these groups had 
advanced to the stage now represented by the Ligulate and 
Rhizecarpee, there is no means of knowing, but that this stage 
was reached in both the great lines during the Carboniferous epoch 
must follow from our hypothesis, since it is within this epoch that 
both the Conifere and the Cycadacee first made their appearance, 
and during which they attained to very much the proportions and 
general character which certain forms of them still present. 
These forms advanced at a parallel rate and both reached the 
point of greatest development and supremacy at about the same 
time in the Triassic and Jurassic periods. They, are both at the 
present time clearly on the decline, especially the Cycadacee, 
which are on the open road to early extinction before the march 
of higher types of vegetation. The palzontology of the Guetacee 15 
little known, but they have been supposed to have originated in- 
the later, Permian, or in the Trias. They constitute at best but a 
transition form, and are not sufficiently abundant to be likely to be 
_ discovered in a fossil state. It is a remarkable fact that the ie : 
remains of both the Wonocotyle and the Dicotyle have been founc a 
