47^ VASCULAR CRYPTOGAMS. 



arise very near the puncium 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 6". Marlensit), 

 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. Marlensu, incEqualifoUa, and levigala), 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 Selagmella cuspidata, 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 ^9. Martensii, they branch even before they 

 reach the ground. These roots are also formed very early, near the puiictum vege- 

 tattonis, 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 Isoeles, 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 {cuspidata and levigatd) 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.] 



