THE HIGHER CRYPTOGAMIA. 201 



has been observed exhibit the same arrangement of the 

 first four cells of the embryo. This arrangement exists in 

 the Rhizocarpeae, the Equisetaceae, and in Isoetes ; and the 

 position of the first cells of the rudiment of the germ-plant 

 at the lower end of the suspensor of Selaginella, is the 

 same. In these cases the primary leafless axis is formed 

 principally by the multiplication of the lowest of the four 

 cells ; of that one namely which is turned away from the 

 mouth of the archegonium. One of the side cells produces 

 the primary indefinite axis of the plant. A third cell forms 

 the first root, if the embryo produces such an organ. Sal- 

 vinia is well known to be generally rootless ; Selaginella 

 does not send out the first root until after the first bifurca- 

 tion of the stem. In this prevailing fact there is such a 

 marked difference between the vascular cryptograms and 

 monocotyledons, that the remarkable similarity between 

 the germ-plants of the Naiadeae and the grasses, and those 

 of the vascular cryptograms (especially such of the latter as 

 have a prothallium devoid of chlorophyll) upon which 

 similarity I once attempted to ground a comparison of the 

 organs of the two families, appears to be an unessential 

 external resemblance. 



The multiplication of the primary cell of the lateral 

 principal shoot considerably exceeds that of the mother- 

 cell of the primary axis. The same thing prevails 

 although in a less degree in the primary cell of the 

 first root. Both divide by means of septa inclined in 

 different directions, and, it would seem, in a manner 

 similar to that in which in the more advanced plant, 

 the multiplication of the cells of the first degree takes 

 place. I recognised the triangular form, when seen from 

 above, of the apical cell of the principal shoot in Aspi- 

 diumfdix-mas, and the two edged form of the same cell, 

 when viewed in a similar manner, of Pteris aqiiilina, 

 after about three divisions had taken place in each of 

 them. Even after the first round of divisions the stem- 

 cell of the first degree ceases to multiply further : * a 

 proportionally more rapid sequence of divisions begins in 



* See the explanation to PI. XXVIII, fig. 3 \ and PI. XXVII, figs. G \ 7 b . 



