222 H0FME1STER, ON 



very probably consists in the occurrence from time to time 

 of the division of a newly formed cell of the second degree 

 by means of a slightly convex longitudinal septum, turned 

 towards the cell of the first degree, which cuts off from the 

 cell of the second degree a daughter- cell, whose form coin- 

 cides with that of the apical cell of the stem (PL XXX, 

 fig. 2). The rudiment of the frond bears considerable re- 

 semblance to the end of the stem in the arrangement of its 

 cells, but is distinguishable by the greater curvature of its 

 arcuate surface, and by the very early appearance, (although 

 at first in small quantity), of chlorophyll in its cells. The 

 growth of the frond in length and thickness is at first very 

 slow. The rapidly elongating apex of the stem soon leaves 

 it behind. Whilst the premature development of its cor- 

 tical tissue commences on the side turned to the young 

 frond, the wall-like elevation of the circumference of the stem 

 in the neighbourhood of the terminal bud pushes itself at 

 an early period into the space between the two. The frond 

 and the end of the stem which at the first appearance of 

 the former are enclosed in the same depression of the bark, 

 are now each of them situated at the base of a special 

 funnel-shaped depression. The tips of the scales which 

 clothe their walls protrude above each depression in a peni- 

 cillate maimer (PI. XXX, fig. 5). 



Whilst the germ-plant in the first year produces as 

 many as twelve slender fronds whose development is con- 

 tinually progressive, the development of the fronds of older 

 plants, which is frequently interrupted by long periods of 

 cessation, requires several years. It is a rule, departed 

 from only in cases of sudden alteration of the conditions of 

 vegetation, (such as the ploughing up of the ground of a 

 wood), that each shoot of the mature plant sends out yearly 

 only one frond.* New fronds are produced towards the 

 end of the vegetative period which lasts from April till 

 October. In the first year the frond assumes no greater 

 development than that of a low, laterally flattened, green 

 wart of cellular tissue, situated at the base of a depression 

 of the bark of the stem, distant at the most not more than 

 a line from the apex of the stem. In the following year 



* See A. Braun, c Verjiingung,' p. 63. 



