meris terns of Ferns as a Phylogenetic Study. 335 
more marked than in the Osmundaceae. Holle 1 has investi- 
gated the apex of the leaf of the Marattiaceae ; but it is not 
clear from his description whether his observations refer to 
Marattia or to Angiopteris , or to both genera. He finds the 
flattened apex of the leaf to be occupied by a single wedge- 
shaped apical cell, which is neither two nor three-sided, but 
of irregular section, and from it segments are cut off without 
regular order : he states that the identity of the apical cell is 
maintained till after the origination of the pinnae. 
An examination of numerous leaves of well-grown plants 
of Marattia fraxinea has led me to the following results : — 
When seen in plan, the apical meristem of a young leaf, as yet 
without pinnae, may show a single three-sided initial cell : 
from this segments are cut off in regular sequence (Fig. 36) ; 
it is, however, to be noted that, as in the case figured, the 
initial cell is of relatively small size, while the growth of its 
segments is relatively rapid : thus in Fig. 36, the fourth 
segment occupies nearly double the area of the other three 
segments and the apical cell together : comparing this with 
Osmunda (Fig. 34) the difference is obvious, for here the area 
occupied by the apical cell and the last three segments is 
distinctly greater than that of the fourth segment : a com- 
parison of the apex of the leaf of Trichomanes (Fig. 30) also 
shows the area of the apical cell in proportion to its segments 
to be much greater. With this relatively more rapid growth 
of the segments than of the apical cell itself is associated 
(as in Osmunda) irregularity of sub-division of the segments : 
each divides, it is true, by a sextant wall into two halves, 
but the further sub-divisions follow no constant rule. Fre- 
quently they present an appearance as though a series of 
segments were cut off from one triangular cell, which thus 
acquires the aspect of an initial cell, and may be styled a 
4 secondary initial 5 : one such is seen in the abaxial half of 
the fourth segment in Fig. 36, and it will be subsequently 
shown that forms and arrangements of cells appear in longi- 
tudinal sections, which bear out the idea that these cells 
1 Bot. Zeit. 1876, p. 218. 
