meristems of Ferns as a Phylogenetic Study . 361 
dividing a basal or stalk cell from the cell which will form the 
head of the sporangium (compare diagram Fig. 88 a , x,x .) : 
this I take to be the simplest segmentation of all. In the 
Hymenophyllaceae 1 , in Ceratopteris 2 , and in Marsilia 3 the 
first segmentation is frequently not transverse, but oblique, 
and this type I take to be nearer to the more complicated 
eusporangiate forms (compare diagram Fig. 88, b ). This is, 
however, only a slight difference of detail ; the main point is, 
that in all these Ferns the sporangium ultimately springs 
from a single superficial cell : in all of them it has been 
demonstrated by the writers above quoted that the position 
and order of succession of the divisions in the head of the 
sporangium show quite a diagrammatic regularity, and it will 
be remembered in connection with this that the structure of 
their apical meristems is comparatively simple and precise, a 
single apical cell with definite mode of segmentation being 
present ; thus in these plants there is a parallelism between 
the structure of the apical meristems and that of the young 
sporangium. 
It has been noted that in the Hymenophyllaceae the basal 
wall (x,x, diagram Fig. 88, b ) is oblique: its position is 
apparently not quite uniform, but it appears usually to meet 
one of the lateral walls of the initial cell 4 ; in the Schizaeaceae, 
however 5 , this basal wall appears to be inserted actually on 
the periclinal (basal) wall of the initial cell (compare x^x, 
diagram Fig. 88, c), and is accordingly more inclined than in 
the previous cases. Though this may appear a trivial detail, 
it is to be noted as an indication of a lowering of the centre of 
construction of the sporangium, and of the assumption of a 
more robust and massive character. Though the sporangium 
of the Schizaeaceae is wholly derived from a single initial cell, 
it is, when mature, relatively large as compared with the other 
leptosporangiate Ferns, and it is seated on a short thick 
1 Prantl, 1 . c. Plate VI, Figs. 103-105, etc. 
2 Kny, Parkeriaceae, Plate XXV, Figs. 2, 3, 5. 
3 Russow, Vergl. Unters. Taf. VI, Figs. 62, 71, etc. 
i Prantl, Hymenophyllaceae, p. 39, Taf. VI, Figs. 100, 104. 
5 Prantl, Schizaeaceae, p. 49. 
