meristems of Ferns as a Phylogenetic Study. 387 
and of the Cycadaceae. There is no apical cell, and apical 
growth is not strongly defined ; periclinal divisions of the 
superficial cells are frequent throughout the leaf, from apex to 
base, but especially on the ventral side ; intercalary growth is 
strongest at first below the ligule, and then diminishes in that 
part and extends to the upper part of the leaf. These charac- 
ters, as well as others, suggest that Isoetes may be a form 
intermediate between Marattiaceae and Cycadaceae, in which 
the vegetative organs have been reduced in structure and ex- 
ternal form in accordance with aqueous habit . 5 Since then, 
Vines 1 has on various grounds arrived at the conclusion that 
the true relation of Isoetes is rather to the Filicineae than to 
the Lycopodineae. Without at present entering upon the dis- 
cussion of this matter at large, it will be well to point out the 
bearing of the observations contained in this paper upon this 
debateable question. So far as they affect the point, they 
strengthen rather than invalidate the suggested grounds of 
affinity of Isoetes to the Marattiaceae. It has been shown by 
Bruchmann that the apices of the roots of Isoetes have a strati- 
fied structure, similar to that which is seen in certain Angio- 
sperms, there being present no clearly defined initial cells. 
The same writer, and also Hegelmaier 2 , point out that the 
apex of the stem is occupied by a small number of initial cells, 
which appear to correspond to the structure found in the 
Marattiaceae. I have also indicated that the characters of 
the leaf are not inconsistent with the suggested position, and 
Hegelmaier 3 also points out that there is no apical cell. As 
regards the form of the leaf, when it is remembered that the 
leaves of the Danaeas are relatively simple in conformation, 
while in D.simplicifolia,'R.\\dgQyhe leaf is actually unbranched 4 , 
it will be seen that comparatively slight simplification of the 
type of leaf would result in such a one as that of Isoetes. 
Taking all the meristematic characters together (and it is with 
them that we are now more especially concerned), the evidence 
offers no serious barrier to assigning to Isoetes the position 
1 Annals of Botany, II, pp. 117, 223. 2 Bot. Zeit. 1875, pp. 485-6. 
8 1 . c. p. 499. 4 Kunze, Die Farrnkrauter, Plate 50. 
D d 
