EXTERNAL CHARACTERS 627 
Osmundaceae and Matonineae, and occasionally in other genera, for instance 
in Cyathea and in Preris. On the other hand, axillary branches are found 
with a high degree of constancy in the Botryopterideae and Hymeno- 
phyllaceae. In other Ferns buds are found in varying relation to the 
leaf-bases, and at various other points upon the leaves: all these appear 
to be different in their nature 
and origin from the terminal, 
dichotomous branches above 
mentioned. 
The architecture of the 
leaves of Ferns, with their 
complex and variable out- 
lines, presents features which 
are important for comparison. 
For long the developmental 
interest centred in the apical 
segmentation, as exhibited in 
the Leptosporangiate Ferns 
with their single initial cell. 
It was not till 1874 that 
Sadebeck extended that in- 
terest to the marginal growth 
of the ultimate pinnules, and 
showed in the case of Asplen- 
zum Shepherdi that the last Fic. 348. 
branchings of the veins are Allosorus crispus. Outline of a leaflet. The branching is 
' 5 ‘ clearly dichotomous. The apex has divided into lobes z and 2 
true dichotomies (Fig. 347) of which 1 is the stronger and continues the growth, 2 forms a 
lateral lobe. Below we have lobes 3 and 4 which have been 
The same was shown later by similarly formed. The leaf-spindle (rachis) S, is only a narrower 
Prantl in the Hymenophyl- gevton, of tho, lamina which is guimetoenty mechanically 
laceae: such dichotomy may 
be held to be wide-spread in Ferns, and its results are apparent in the 
external outline of many young leaves; for instance, it cannot be missed 
in the case of Allosorus crispus, quoted by Goebel (Fig. 348): here the 
successive pinnules are produced as branches of a dichotomy, and are 
successively relegated to a lateral position right and left: the whole pinna 
is thus a sympodial development of a dichotomous system, though when 
mature it presents an appearance of pinnation. 
Dichotomous branching is a very obvious feature even in the mature 
leaves in some of those Ferns which are believed to be relatively primitive. 
For instance, in the Schizaeaceae, and especially in Schizaea itself, while 
the same is seen with modifications in the pinnae of Zygodium. Again, 
in Matonia and Dipieris it is very obvious, though with sympodial develop- 
ment of the branches; and in the Hymenophyllaceae, especially in the 
1See Prantl, Unters. « Morph. d. Gefisskryptogamen. J. Die Hymenophyllaceen 
Die Schizacaceen. 
