476 
VASCULAR CRYPTOGAMS, 
consist, in /. lacus/rts, of only a small lamina, but in the terrestrial species are 
destitute even of this, and are simply cataphyllary leaves (phyllades). 
The leaves of Selaginella are never more than a few millimetres in length, and 
are usually cordate at the base with a narrow insertion, acuminate, and from lanceo- 
late to ovate in form. In the greater number of species the sterile leaves are of two 
different sizes, the ventral leaves attached to the under or shaded side of the 
obliquely ascending stem are much larger than the dorsal leaves on the upper side 
exposed to the light (Fig. 335, A). Both kinds taken together form four longi- 
tudinal rows {vide infra). On its upper side and near the base each leaf bears a 
ligule ; the point of attachment of the sporan- 
gium is below this on the fertile leaves. The 
fertile leaves form a quadrangular terminal spike, 
are uniform in size, and usually of somewhat 
different form from the sterile ones. 
Phyllotaxis. In Isoetes the rosettes are ar- 
ranged spirally, with the divergences f , -f^, 
"If, the fractions becoming more compHcated 
the larger the number of leaves that are an- 
nually formed. In the species of Selaginella 
which have their leaves arranged in four rows, 
each dorsal and ventral leaf form together a 
pair, whose median plane, however, does not 
intersect that of the next pair at right angles 
but obliquely, an arrangement which is often 
clearly seen on old shoots of S. Kraussiana. 
The Apical Growth of the stem takes place 
by means of an apical celP. That of Isoetes 
lacusii'is is, according to Hofmeister, two-edged 
when the stem has two furrows ; in the species 
with three furrows it is a three-sided pyramid. 
In young plants the leaves stand accordingly 
in the first case in two, in the second case in 
three rows; but later the phyllotaxis becomes 
more complicated and spiral, indicating perhaps 
that in the older stem the primary walls of the 
segments advance in the anodal direction, as is 
the case in those Mosses which have a three- 
sided apical cell and a complicated phyllotaxis. In those species of Selaginella which 
have the leaves in four rows, the apical cell of the stem is, according to Pfeffer, two- 
Fig. 335. — Selaginella iiiisqnalifolia ; A fertile 
branch (one-half natural size) ; B apex in longitudinal 
section bearing- microsporangia on the left, macro- 
sporangia on the right (magnified). 
^ [Hegelmaier (Bot. Zeitg. 1874) was unable to find an apical cell in Isoetes velata or in 
7. Burieui. He considers that, since in certain Selaginellese {S. arhorescens, Pervillei, Lyallii ; Russow, 
Vergl. Unters.) there is not a single apical cell, but a group of dividing cells, and in S. Wallichii 
(Strasburger, Bot. Zeitg. 1873) there are two apical cells, whereas in the other Selaginelleae there is 
a single apical cell, it is possible that similar differences may exist in the genus Iso'etes; some species 
having a single apical cell, and others a group.] 
