EMBRYOLOGY 649 
absent as a matter of fact in many of the Simplices in their mature state, 
and apparently from all Ferns in the first condition of the seedling. 
The vascular structure thus held to be ‘primitive and typical for Ferns 
is that characteristic of strobiloid plants, and it seems reasonable to read 
the anatomical data as indicating that the Ferns also are essentially 
strobiloid, but have progressed to a condition of megaphylly, while the 
anatomical characters that ultimately accompany that habit lagged behind 
in the several evolutionary series, and only become apparent in the later 
representatives of each. 
EMBRYOLOGY. 
The primary embryology of Ferns shows so nearly a dead level of 
uniformity that it has not seemed necessary to describe the details for 
the successive families. There are, however, two distinct types: that of 
Fic. 351. 
Transverse sections through growing point of root in Osmundaceae. A=Ossunda 
regalis; the section shows a three-sided initial (7), but the segments are not regular. 
B=shows transverse section immediately below the root-cap; three initials (7, x) are 
present ; the dotted line is the cell-division in the root-cap, seen on focussing deeply into 
the hand-cut section; this shows that the section has traversed the initials and Is not 
below them. C= Todea barbara, showing a very regular meristem of the root, with four 
initials (x, «). 144. 
the Marattiaceae, and that of the main series of the Leptosporangiate Ferns, 
and these must be compared. The most obvious difference lies in the 
fact that the seedling of the Marattiaceae perforates the prothallus, and 
emerges with an upright axis through its upper surface (see Fig. 292, p. 527): 
that of the Leptosporangiate series emerges on the lower surface, and the 
axis is at first prone (see Figs. 14, 15, pp. 30, 31). This difference may 
be referred back to the first segmentation of the zygote, and appears to be 
closely related to the difference of polarity then initiated; for in the 
Marattiaceae the first wall appears at right angles to the axis of the 
archegonium, but in the Leptosporangiates it is approximately in a plane 
including the axis. The further segmentation, and the relation of the 
parts of the embryo to the first divisions are substantially alike in both: 
except that in the Marattiaceae, as also in the Osmundaceae, there is a 
less regularity in the later divisions than is the case with the other Lepto- 
sporangiate Ferns. In this respect Osmunda occupies an intermediate 
position between the latter and the ‘Marattiaceae. The parts formed in 
