250 HOFMEISTER, ON 



pestris to about the sixth, in N. splendens as far as the 

 third cell from the apex, reckoning backwards. The upper- 

 most cells of the frond, those into which the above division 

 does not extend, now expand considerably lengthwise, 

 the expansion commences with the apical cell and the 

 others follow step by step (PL XXXII, figs. 13, 14). The 

 termination of the multiplication of these cells is mani- 

 fested by the thickening of their walls, and by their con- 

 tents becoming transparent. On the other hand a partial, 

 very considerable multiplication, ensues in the remaining 

 cells of the frond. It is most considerable in the cells at 

 the base, where the divisions by means of septa at right 

 angles to the longitudinal axis of the frond are most fre- 

 quently repeated, alternating with divisions parallel to 

 such axis. The activity of the cell-multiplication dimi- 

 nishes continuously towards the apex of the frond. The 

 divisions first cease in the cells of the upper half of the 

 frond, which become elongated at the earliest period and to 

 the greatest extent. The division of the cells of the 

 frond by means of septa parallel to the longitudinal axis, 

 appears not to be contemporaneous ; it is repeated oftener, 

 and 'extends nearer to the apex of the frond in one longitu- 

 dinal moiety of the frond than in the other (PI. XXXIII, 

 fig. 8). 



Owing to the gradual increase in breadth of the base of the 

 frond, its cells in Niphobolus rupestris, Nephrolepis splendens, 

 and Polypodium aureum, do not amalgamate with the cells 

 of the circumference of the stem with which they are in 

 contact. The place of attachment of the frond does not 

 become wider, and moreover consists, even when the frond 

 is perfected, of only two cells, which have been produced 

 by the division by means of a longitudinal septum of the 

 undermost cell of the rudiment of the frond. The cells 

 of the free margin of the base of the frond multiply actively 

 in many species (as for instance in Niphobolus rupestris 

 and N. splendens), through division by means of septa 

 parallel to a tangent to the circumference; those cells 

 which adjoin the place of attachment of the frond and the 

 angle of the lateral margins multiplying less actively than 

 those between them. The base of the frond thus becomes 



