meristems of Ferns as a Phylogenetic Study. 3 1 9 
a narrow, three-sided pyramid. Sachs 1 figures and describes 
the apical cell of this plant as a two-sided one, and sum- 
marises the knowledge acquired on this point thus : — ‘ We 
may for the present take it to be the rule that creeping stems 
with bilateral structure have a two-sided apical cell, and that 
in erect or ascending stems with rosettes of leaves radiating in 
every direction, the apical cell is a three-sided pyramid.’ But 
the wide observations on the apices of dorsiventral Ferns by 
Dr. L. Klein 2 clearly disproved this generalisation : he inves- 
tigated fifty species, belonging to nineteen genera, with the 
result that, excepting Pteris aquilina , all had a three-sided 
initial cell at the apex of the stem : further, Klein found 
that the form of the apical cell is variable in Pteris itself. 
Even in Ceratopteris , with its thin and elongated apex, 
a three-sided initial cell is present 3 , though it might have 
been anticipated that in so slender a form the construc- 
tion might have been simpler : the stem however is upright, 
and the leaf-arrangement spiral. Passing to the Hydro- 
pterideae, in Azolla 4 , and in Salvinia 5 , the apex of the rhizome 
has been shown to be occupied by a two-sided cell, with 
segments alternating on opposite sides; in Marsilia however 6 
there is a three-sided cell : the same appears to be also the 
case in Pilularia , according to my own observations, and 
Campbell 7 appears to have come to the same conclusion, for 
though he does not state the fact directly, he allows it to be 
inferred, since he speaks of a c third or ventral segment there 
is in fact a difference in the structure of the apex of the stem 
between the two sections of the Heterosporous Filicineae, the 
more distinctly aquatic forms being the simpler. Thus obser- 
vations on a large number of leptosporangiate Ferns have 
shown that whether the stems be dorsiventral and creeping, or 
radial and erect, the apex is occupied by a three-sided pyra- 
1 Textbook, 4th German edition, p. 423. 
2 Bot. Zeit, 1884, p. 577. 
3 Kny, Parkeriaceae, p. 28. 4 Strasburger, Ueber Azolla , p. 17. 
5 Pringsheim’s Jahrbiicher, IV. 
6 Hanstein in Pringh. Jahrb. IV, Taf. XIV, Figs. 4, 5. 
7 Annals of Botany, II, p. 260. 
