THE HIGHER CRYPTOGAMIA. 203 



to one another in JPteris aquiima), so that the cell retains 

 its original two-edged form ; and three times by means of 

 flat septa diverging from one another at angles of 60, so 

 that the cell assumes the shape of a three-sided pyramid 

 with an arched under surface (Pl.XXVl,fig. 6). In both cases 

 a septum is now formed parallel to the chord of the outer 

 arc (PL XXVIII, fig. 1 ; PL XXVI, fig. 7). The flat cell cut 

 off by this latter septum is the first rudiment of the root- 

 cap, whose outermost, hood-shaped, cellular layer is formed 

 by the multiplication of this cell. Henceforth the root- 

 cell of the first degree lies surrounded by cellular tissue. 

 Its further increase arises from repeated divisions occurring 

 in the same succession. 



> Judging from its position, the first root of the young fern 

 is adventitious, differing in no respect from the later 

 adventitious roots of the full-grown plant. This view of 

 the nature of the first root of the vascular cryptogams in 

 general (a view which I expressed many years since*), 

 has lately been objected to by Wigand. His first objec- 

 tion (an unfounded one) rests principally upon a con- 

 jecture that the foot-shaped portion of the germ-plant, that 

 which I have called the primary axis, not only amalgamates 

 with the prothallium, but is probabh/ prolonged backwards 

 so as to form the root. Wigand adds, " I consider that 

 the enlargement of the lower part of the germ-plant is of a 

 different nature ; I look upon it as the undoubted rudi- 

 ment of the first main root; it does not break through 

 after the manner of an adventitious root." A few words 

 of explanation are requisite as to the distinction be- 

 tween main roots and adventitious roots in general. 

 Our conceptions of main roots rest entirely upon the 

 observation, that the portion of the embryo of dicotyle- 

 dons, which is situated beneath the cotyledons (and in 

 most instances that portion of the plant alone) is prolonged 

 downwards and becomes the root, and that in a normal 

 state no portion of the plant above the cotyledons sends 

 forth roots. Now, strictly speaking, the root by no means 

 commences close underneath the insertion of the cotyledons, 

 for between the latter point and the root there is to be 

 * Berliu 'Botanische Zeitung,' 1849, 797. 



