THE HIGHER CRYPTOGAMIA. 213 



angles to the axis, on account of the rapid horizontal 

 longitudinal grow.th of the stem, which far outstrips the 

 development of the frond ; and the result is that the sur- 

 faces of the frond are parallel to the axis. The stalks even 

 of the first fronds exhibit the appearance* which occurs in 

 the stipes of almost all fronds, that is to say, prominent 

 bands of loose cellular tissue having the intercellular cavi- 

 ties filled with air pass along the side edges of the stipes ; 

 which bands are in connexion with, and of the same nature 

 as, the inner parenchyma, which latter, except where it is 

 traversed by the bands, is enclosed by a firm cortical 

 tissue (PI. XXX, figs. 7, 9). The creeping stem of Pteris 

 aquilina (PI. XXX, fig. 3), and the stems of the exotic 

 DicksoniEe, which are similar in their habit, exhibit the same 

 quality. The lateral ridges of the stem pass directly into 

 those of the fronds (PL XXIX, fig. 14). 



At an early period the germ-plant exhibits that prema- 

 ture vigorous development of the peripheral cellular layers 

 of the stem in the immediate neighbourhood of its terminal 

 bud, which afterwards has a marked effect upon the form 

 and position of the apex of the stem. The growth in 

 thickness of the cortical tissue of the next younger portion of 

 the stem is very rapid, and by the time that the third 

 frond is developed, the apex of the stem appears to be 

 sunk in that tissue (PI. XXIX, fig. 6). 



The internal structure of the young stem, like that of the 

 first frond, is very simple. Prom the point of junction of 

 the vascular bundles of the first frond and first root there is 

 developed a central vascular bundle, traversing the young 

 stem (PI. XXIX, figs. 5, 6, 7), from which the transformation 

 into vascular bundles of the strings of cellular tissue which 

 pass into the newly-formed fronds commences, and on the 

 outer surface of which the development of new adventitious 

 roots begins (PI. XXIX, fig. 6). The direction of the second 

 and of the next following root diverges by about 90 from 

 a plane passing through the first frond and the longitudinal 

 axis of the stem (PL XXIX, fig, 6). The subsequent 

 roots exhibit no trace of this regular arrangement. 



After the formation of from seven to nine fronds, the 



* Karsten, ' Vegetations-organe der Pahuen,' p. 129. 



