412 VASCULAR CRYPTOGAMS. 



above ground. The root-like shoots branch like the ordinary ones ; a cell is cut 

 off by an oblique wall from one of the youngest segments, and forms the apical 

 cell of the new shoot. 



All the species of Selaginella possess true roots ; but in some, as S. Martensii 

 and Kraussiana, they arise on a structure which Nageli calls the Rhizophore, and 

 which has no root-cap. In S. Kraussiana the rhizophores spring from the dorsal 

 side of the stem, nearly at the base of the weaker fork of each dichotomy, curl 

 themselves round it, and then grow downwards ; it is only rarely in this species that 

 two of these organs arise near one another. ^. Martensii, on the other hand, forms 

 at each fork two rhizophores, one on the dorsal and one on the ventral side (the 

 plane which passes through them is perpendicular to the plane of dichotomy), but 

 usually only the ventral one undergoes further development, while the dorsal 

 generally remains in the form of a small protuberance. The rhizophores arise 

 very near the piindum vege/ationis, probably at the same time as the branches 

 of the dichotomy ; unlike the roots, they are exogenous structures which, when 

 young, possess a distinct apical cell. This is probably two-edged, but soon 

 ceases to form new segments, the further growth being effected by intercalary 

 divisions of the segments and elongations of the cells w^hich 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. Martensii, i7icBqualifolia, and levigata), are often transformed into true 

 leafy shoots, which at first show some deviations from the normal structure in their 

 first leaves, but afterwards continue to grow as normal shoots, and even produce 

 sporangiferous spikes. 



In Selaginella Kraussiana, cuspidata, and some other species, there are no 

 rhizophores, but the roots spring immediately from the places nearest the ground 

 where the stem forks and dichotomises, like the rhizophores of S. Martensii, even 

 before they reach the ground. These roots are also formed very early, near the 

 pundum vegetationis, 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 dichotomously, and in such a manner that the planes of the 

 successive dichotomies 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-edged. It soon ceases to form segments ; the increase 

 of length of each fork 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 dichotomise 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 exist- 

 ence of a two-edged apical cell probable. In Ljropodium davaium the roots spring 



