4 
i 
1878.] On the Genealogy of Plants. ` 373 
dence of a transition in the rudimentary ovary, would seem at ° 
first view to afford no pltysiognomic mark to indicate the point 
at which the chasm was bridged over. There is one family of 
Dicotyledons, however, which, though little familiar to the inhabi- 
tants of the northern hemisphere, are none the less likely to have 
completed this transition, and in which there certainly is a strong 
physiognomic resemblance to at least one genus of the Guetacee. 
Humboldt} speaking of the remarkable form of the Casuarinee 
of the East Indies, describes them as “trees with equisetum-like 
branches,” and remarks that “ Plumier’s Equisetum altissimum, and 
Forskal’s Ephedra aphylla of North Africa, are forms nearly allied 
to Casuarina.” This physiognomic resemblance of Ephedra to 
both Casuarina and Eguisetum is certainly very interesting, not 
only as affording a provisional hypothesis for explaining the 
transition from the Gymnosperms to the Dicotyle, but also as 
marking out a line of investigation with a view to determining 
the origin of the Guetacee. But to this we shall revert. 
Not only do the Guetacee thus approach the Dicoty/e in their 
reproductive system, but they also present a corresponding 
advance in the formation of the secondary wood from the struc- 
ture of the Conifere towards that of the true Exogens. Besides 
the wracheides of the former it also contains vessels closely 
resembling the porous ducts of the latter. 
Should the descent of the Dicotyle from the Guetacee be 
accepted as probable, it would only remain to determine the origin 
of the latter in order to complete a rough outline of the entire 
genealogy of vascular plants. 
As already remarked, the attempt to affiliate them upon the 
Equisetacee, as a third independent branch of the Cryptogams, 
cannot be seriously made in the present state of science, not- 
withstanding the singular harmony in the general aspect of 
Ephedra and Equisetum. The fact heretofore pointed out, how- 
ever, that a striking analogy subsists between the spikes of Egui- 
setum and the male aments of Taxus and other allied genera, 
may be taken as a faint indication of what may have been the 
mode of development of these forms. It should at least be 
remarked that within the Conifere there is exhibited no small 
degree of progress towards certain leading characteristics pos- 
sessed by the Dicotyledons. From the lowest to the highest, oo a 
_ lAnsichten der Natur, Stuttgart, 1871, p. 137- 
