230 EVIDENCE FROM PALAEOPHYTOLOGY 
are clearly apprehended that the true value of that evidence will begin to 
emerge. Though, as we see, it cannot yet be held to throw any direct 
light on the prime origin of terrestrial plants, still it has valuable bearings 
on the mutual relations of the earlier known types. It is especially valid 
‘in supplying a knowledge of “synthetic types,” that is, plants now extinct, 
which include among their characteristics some of the peculiarities of two 
or more distinct lines of descent. The most important of these hitherto 
disclosed are the Sphenophylls, which constitute a series separate from the 
three great phyla of living Pteridophytes, though some affinity is to be 
recognised between them and the modern Psilotaceae. Their leaves agree 
with those of the Equisetales in being whorled, and being superposed 
they are most nearly like the oldest known Calamite—Archaeocalamites. 
Their whorled arrangement also corresponds with that of one of the 
earliest Lycopods, Lycopodites Stockii, from the calciferous sandstone. 
The anatomy of the stem of Sphenophyllum is Lycopodial rather than 
Equisetal, but the strobili are nearer to those of the Equisetales than to those 
of any other known family. The interest in the group which showed such 
mixed characters was further intensified by the discovery of Cheivostrobus.) 
“This strobilus presents the same combination of Lycopodial’ with Equi- 
setal characters which we find in Sphenophyllum itself, but in both directions 
the agreement is more striking. .. . We may express its probable natural 
position by placing it in the main division Sphenophyllales, but in a 
family by itself, distinct from the Sphenophylleae in the narrower sense. 
The threefold affinities of Cheirostrobus, firstly with the Sphenophylleae, 
secondly with the Equisetales, and thirdly with the Lycopodiales, appear 
indisputable, and indicate that this genus, and the Sphenophyllales gene- 
rally, represent a phylum intermediate between the other two, which we 
must suppose to have originated with them, from a common ancestral 
group. In this way, the study of the extinct Sphenophyllales has thrown 
quite a new light on the obscure affinities of the Equisetal stock, for it 
indicates clearly that this phylum had a common origin with that of the 
Lycopodiales, a conclusion which the exclusive investigation of their recent 
representatives could never have suggested.” Another important synthetic 
group of plants, of early occurrence, is that of the Cycadofilices, which 
link together the Pteridophytes and the Gymnosperms. Such examples 
illustrate what may be held to be the most important results obtained 
hitherto from Palaeophytology, as aiding the study of descent in Plants. 
Another line of argument from Palaeontological data is now beginning 
to be used, though only sparingly, since it is rare as yet to find that the 
facts suffice for its application. It consists in the comparison of plants of 
near affinity from different strata, and deducing from their stratigraphical 
sequence a progression as regards some single character. This method 
has been carried out successfully by Mr. Kidston, in respect of the structure 
of the stele of Lycopods: he has concluded that “it is probable that the 
1See Scott, Studies in Fossil Botany, pp. 494-497. 
