252 



THIRD GROUP. VASCULAR CRyPTOGAMS. 



great height ; it is tuber-iike in form and is partly buried in the ground, and is so 

 covered with leaves that no part of the surface is free. In some species this tuberous 

 stem remains comparatively small, in the large Marattiae and in Angiopteris evecta it 

 may be of considerable circumference and from one to two feet high. The stem of 

 Kaulfussia assamica is, according to De Vriese, an underground creeping dorsiventral 

 rhizome, with leaves on the upper and roots on the under side ; that of Danaea 

 trifoh'ala, as we learn from Holle, is rather long and branched, and the leaves so far 

 differ from the leaves of other species that they have no stipules at the base of the 

 petiole. The stem of the Marattiaceae, Danaea excepted, like that of the Ophioglosseae 



tl 



FIG. 205. Vertical longitudinal section of the stem of a young plant of Angiopteris evecta ; b the youngest 

 leaves still quite covered up by the stipules nb, st stalk of an unfolded leaf with its stipula nb, n everywhere the leaf- 

 scars on the basal portions ff, from which the leaf-stalks have separated, cc the commissures of the stipules in longitu- 

 dinal section, ww the roots. Natural size. 



and Isoeteae, appears never to branch. The lower and older region of the stem is 

 covered with the basal portions of the older petioles bearing the stipules, and from 

 these portions the upper parts of the petioles, provided at this point with large 

 cushion-like swellings (pulvini), have fallen away, leaving behind them a broad smooth 

 flat scar girt with the stipule (Fig. 205 ;?) ; the upper part of the stem bears a large 

 rosette of living leaves, in the centre of which is the bud composed of rather 

 numerous young leaves of all ages (b, nb}. The leaves in the bud are circinately 

 rolled up, and are completely enveloped by the stipules till the elongation of the petiole 

 and the unrolling of the lamina begins ; each pair of stipules belonging to a petiole 



