460 
VASCULAR CRYPTOGAMS. 
apical cell of the stem forms two rows of segments, a right and a left. Sori either male 
or female : each sorus contained in a unilocular sporocarp. Spores invested by hardened 
frothy mucilage (Massulae, Epispore). The prothallium derived from the macrospore 
is well developed and bears several archegonia. JlzoUa has roots, Salvinia has none. 
Family 2. MarsiliaceaB. Plants creeping on moist earth, or floating to some extent 
in water. The three-sided apical cell of the stem forms two dorso-lateral rows, and 
one ventral row of segments. Each sorus includes both macro- and microsporangia, 
and two or more sori are contained in the multilocular sporocarp. The spores are in- 
vested by hardened mucilage — epispore — which presents a radially prismatic structure, 
and is to some extent capable of swelling-up. The prothallium of the macrospore bears 
a single archegonium. This family includes the genera Marsilia and Pilularia. 
CLASS IX. 
DlCHOTOME^ ^. 
Hitherto the Lycopodiese, Psilotum, the Selaginellae, the Isoetege, etc., have 
been included together in the group of the Lycopodiaceae, and rightly so, for 
these genera exhibit not only in their habit, but also in their morphology, a degree of 
relationship which makes it impossible to separate any one of them from the others 
with the view of erecting it into a new class or of including it in one of the other 
two classes of Vascular Cryptogams. Recent investigations have, however, shown 
that this class includes two well-defined subdivisions which must be kept distinct. 
To one of these two orders belong the genus Lycopodium and its immediate allies, 
and it must therefore necessarily take the name of Lycopodiacese ; consequently 
a new name has to be found for the whole class, and I select that of Dichotomeje, 
because it brings into prominence one of the most obvious of the characteristics 
of these plants, that the branching presents the appearance of being the result of 
dichotomy, although, as a matter of fact, the branching of the stem is monopodial. 
It must be remembered, however, that these two modes of branching gradually pass 
one into the other. These plants are as remarkable among vascular plants for their 
evident tendency to branch dichotomously as are the Equisetaceae for their whorls of 
leaves. That dichotomy is indeed a typical peculiarity of these plants is proved by 
the fact that their roots are the only ones at present known which branch 
dichotomously. 
The dichotomous habit of the branching is by no means the only characteristic 
common to the members of this class, as a comparison with the Equisetaceae and 
Filicinese at once shows. They possess but little in commiOn with the Equisetaceas 
except perhaps the relatively slight development of the leaves, although that is 
brought about in this class in a very different way, for the similarity in the mode of 
development of the sporangia in the two classes does not merit consideration since, 
as we have seen in the Filicineae, this is a characteristic which is critical only for the 
* [Inasmuch as dichotomous branching is not universal even among the Lycopodiese, many 
authors prefer to designate this group of plants as Lycopodinae.] 
