332 Bower . — The comparative examination of the 
first instance from the central portion of each segment, 
occupies the entire margin of the phyllopodium, pinnae, and 
pinnules. 
Such observations as have been made on the development 
and apex of the leaves of Ferns have been chiefly on the 
Polypodiaceae ; in face of the precise descriptions of Sadebeck *, 
Klein 1 2 , Luerssen 3 , etc., it seems unnecessary to go further than 
recapitulate the general conclusion that the apex of the leaf 
is at first occupied by a two-sided wedge-shaped apical cell, 
from which segments are cut off alternately on opposite sides ; 
that the central part of each segment contributes to the 
marginal series of cells, which is continuous up to the apex, 
and over the apex after the identity of the apical cell is lost : 
thus in most points there is similarity in the apical meristem 
to that of the Hymenophyllaceae, though the resulting frond 
is as a rule more robust. Klein mentions and figures 4 certain 
exceptional arrangements of the segmentations in young 
leaves of the Polypodiaceae. He points out that the apical cell 
is not always from the first a regular two-sided one, but that 
sometimes, the second wall only meeting the first on one side, 
a three-sided initial is temporarily present ; this form may in 
some cases be maintained for a considerable time 5 , but 
always passes over ultimately into the two-sided form. We 
shall see that this condition, which is only temporary and 
exceptional in the Polypodiaceae, becomes typical in the 
Osmundaceae, in which a three-sided initial is constantly 
present. 
Observations were also made on the origin and apex of 
the leaves of Amphicosmia ( Hemitelea ) Walker ae , Hk., and it 
was found that the leaves originate laterally on the apex, in 
almost simultaneous whorls of three, the successive whorls 
alternating with one another. The first appearance of the 
leaf is just as in other leptosporangiate Perns, by outgrowth 
of a single superficial cell, which becomes convex, and is 
1 Schenk’s Handbuch, I, p. 270. 2 Bot. Zeit. 1884, p. 585, etc. 
3 Handbuch der Syst. Bot. I, p. 51 1. 
4 1. c. p. 486, and Figs. 2, 7, 21, 23, 26, 36. 
5 1. c. Figs. 11, 22. 
