meristems of Ferns as a P hylogenetic Study. 307 
gium originates only from a single cell, and those in which it 
has a pluricellular origin, it would be a mistake to accentuate 
this distinction, for it will be seen below that the Fili- 
cineous series leads from the one type to the other by 
gradual steps, and it is only among Filicineae that leptospo- 
rangiate forms are known. Further, it will be shown that as 
we pass along the series of Ferns from the leptosporangiate to 
the eusporangiate forms, an increase of complexity of structure 
more or less marked is to be seen, not only in the sporangium, 
but in every one of the meristematic tissues : in fact, that the 
progress in complexity from the leptosporangiate to the 
eusporangiate Ferns not only involves the increased bulk and 
robustness of the sporangium, but may be taken as an indi- 
cation of a more bulky type of development of all the parts of 
the plant : it will be shown that just as in passing along the 
series the sporangium of unicellular origin in the Hymeno- 
phyllaceae and Polypodiaceae becomes the massive sporan- 
gium ot Marattia, so also as we review the series, we pass from 
the root with one clearly defined apical cell to that with several 
initials, while a similar transition from a simple to a more 
complex construction is to be noted in the apices of stem, 
and leaf, and even in the mode of origin of the wings of the 
leaves. 
The above remarks will suffice to indicate the general scope 
of the present memoir : the theoretical considerations which 
will follow from this comparative study of the meristems of 
Ferns will be deferred to the concluding paragraphs. 
In order to bring out the more clearly the fact that the 
progress from the simpler to the more complex is exemplified 
in each of the meristems of root, stem, leaf, wing, and sporan- 
gium, each of these parts will be dealt with separately, and 
their characters traced in a series of examples, and it may be 
stated that, with few exceptions, the same species have been 
used for the investigation of each of the above-named parts. 
So as to preserve some uniformity of treatment, the forms 
investigated will be taken in regular sequence ; the Hymeno- 
phyllaceae first, because of their greater simplicity of con- 
Y 
