476 



VASCULAR CRYPTOGAMS, 



consist, in /. lacus/n's, 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. 



PhyUolaxis. In Isoetes the rosettes are ar- 

 ranged spirally, with the divergences f, yV> yt* 

 ^f, the fractions becoming more complicated 

 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 cell ^ That of Isoetes 

 lacustris 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 incequali/olia ; 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. Diirieui. He considers that, since in certain Selaginellese (S. arborescens, 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 Selaginellese there'is 

 a single apical cell, it is possible that similar differences may exist in the genus Isoetes; some species 

 having a single apical cell, and others a group.] 



