THE HIGHER CRYPTOGAMIA. 211 



underneath the terminal bud, — which in the meantime has 

 become developed into a cellular wing, — form a connected, 

 slightly curved, string of cambium, upon which the wing is 

 attached sideways (PL XXIX, fig. 1). 



Now whilst the cellular layers surrounding the embryo 

 are ruptured by the longitudinal growth of the frond and 

 root, the cells of the primary axis also become consider- 

 ably elongated, so that the germ-plant is removed from 

 the prothallium as if borne upon a short stem ; an appear- 

 ance which brings to mind the normal process in Salvinia, 

 The innermost cells of the primary axis adjoining the vascular 

 bundles of the frond and of the root assume a prosenchy- 

 matal form (PL XXIX, fig. 1), and at a later period become 

 woody scalariform cells, so that the ligneous body of the 

 germ-plant has a blind-ended short prolongation reaching 

 into the primary axis. 



The growth of the stem-bud, which is rapid in com- 

 parison with what occurs in other ferns, and which is 

 observable whilst the embryo is yet enclosed (PL XXVIII, 

 figs. 4, 5), increases still more after the latter has emerged 

 from the prothallium ; the end of the stem becomes a 

 somewhat slender cone (PL XXIX, fig. 1). The forma- 

 tion of the second frond commences even before any 

 thickenings of the membrane make their appearance in any 

 of the cells of the rudimentary vascular bundles of the 

 germ-plant. The second frond originates in the multipli- 

 cation of a cell of the apex of the stem situated on that 

 side of it which is turned away from the point of attach- 

 ment of the first frond, and distant from the latter by about 

 half the circumference of the stem. The cell-multiplication 

 of the second, and of all the subsequent fronds, follows the 

 same rule as that of the first : it begins by the continually 

 repeated division of the cell of the first degree, by means 

 of septa inclined alternately towards and away from the 

 top point of the stem. After the rudiments of the stipes 

 of the frond are fully formed, the apical cell divides by 

 longitudinal septa at right angles to the fore and hind 

 surfaces ; in all the cells of the thus expanded fore-edge, 

 division occurs by septa inclined alternately towards the 

 upper and under surfaces of the frond. 



