478 
VASCULAR CRYPTOGAMS. 
arise very near the punctum vegetationis^ probably at the same time as the branches ; 
unlike the roots, they are exogenous structures, which, when young, possess a 
distinct apical cell. This is probably two-sided (it is four-sided in S. Mariensn), 
but soon ceases to form new segments, the further growth being effected by 
intercalary division of the segments and elongation of the cells which proceed from 
them. After the cessation of the apical growth, the end of the still very short 
rhizophore swells up into a spherical form ; its cell-walls become thicker, and in 
the interior of the swelling the first rudiments of the true roots originate, which 
however do not break through until the rhizophore has attained such a length by 
intercalary growth that its swollen end penetrates into the ground. The cells of this 
terminal part become disorganised and deliquesce into a homogeneous mucilage, 
through which the true roots penetrate into the ground. The rhizophores, as Pfeffer 
has shown (in S. Martensu, incBqualifolia, and levigata), are often transformed into 
true leafy shoots, which at first show some deviations from the normal structure in 
their leaves, but afterwards continue to grow as normal shoots, and even produce 
sporangiferous spikes. 
In Selaginella cuspidala, and some other species, there are no rhizophores, but 
roots spring immediately from the places nearest the ground where the stem 
branches, and, like the rhizophores of -.S". Afartensii, they branch even before they 
reach the ground. These roots are also formed very early, near the punctum vege- 
tatiom's, probably at the same time as the branches of the stem. The roots which 
spring immediately from the stem, as well as those which proceed from the 
rhizophores, branch in such a manner that the planes of the successive branchings 
cross one another at right angles. The branchings of the roots follow one another 
very quickly, and at the end of the mother-root are densely crowded ; the apical cell 
is difficult to detect, but is probably, like those of the stem and of the rhizophore, 
two-sided (four-sided in -S\ Martensii). It soon ceases to form segments ; the 
increase of length of each branch of the root takes place therefore almost exclusively 
by intercalary growth. Similar phenomena are observable in the roots which 
proceed from the furrows of the stem of Isoetes, and which branch (by true 
dichotomy) three or four times in planes at right angles to one another. Nageli 
and Leitgeb failed to find in them any apical cell distinguished by its form or size, 
although they considered the existence of a two-edged apical cell probable \ (See 
Fig. 138, after Hofmeister.) In Isoetes the plane of the first dichotomy is parallel 
to the axis of the stem, in Selaginella {cusptdata and levigata) the plane of branching 
is at right angles to it. 
The Sporangia of the Ligulatae are of considerable size in proportion to the leaf, 
and are borne on short thick stalks. Each fertile leaf bears a single sporangium 
which always lies below the ligula either on the leaf itself [Isoetes), or in its axil, or 
even on the stem {Selaginella). 
The sporangia of Isoetes are sessile in the fovea of the leaf-sheath, to which 
they are attached by a narrow base (Fig. 334, A). They are unquestionably 
products of the leaves ; the outer leaves of the fertile rosettes produce only macro- 
* [According to Bruchmann, there is not a single apical cell, but a meristem resembling that of 
some. Phanerogams.] 
