of Marattia Douglasii , Baker . 1 1 
true of Angiopteris , as well) the cotyledon originates from one 
of the inner quadrants, and as we shall see, grows up through 
the prothallium instead of from the under side, as in other 
ferns. The young embryo retains a nearly oval outline even 
after it has reached a considerable size, and the external 
differentiation of the members arises much later than is 
usually the case. This lateness in the development of the 
organs is correlated with a correspondingly late differentiation 
of the primary tissue-systems. 
As might be expected, Marattia agrees in the early 
embryonic stages most nearly with the closely related 
Angiopteris. Osmnnda comes nearest it among the other 
ferns in the late establishment of the primary organs and 
tissues, and in both these respects, seems to stand between 
the Marattiaceae and the true Leptosporangiatae. Isoetes 
resembles Marattia quite closely in the early divisions of the 
embryo and the absence of a definite apical cell in the 
cotyledon ; but the position and origin of the stem-apex of 
Isoetes differ from all other Pteridophytes, and have their 
nearest approach among the Monocotyledons. 
The Cotyledon. 
The cotyledon arises from the anterior pair of epibasal 
octants, and in the earlier stages seen showed no definite 
apical cell. The growth is at first nearly vertical, but very 
soon growth on the upper side is much stronger and the leaf 
becomes strongly bent over. Vertical sections of an embryo 
at this stage show that the tissues are already beginning to 
be distinguishable (Fig. 29). A little later the conical 
cotyledon becomes flattened towards the end so that the 
lamina becomes differentiated, and this is accompanied by 
a dichotomy of the lamina, which is repeated (Fig. 34), so 
that at the time the young plant breaks through the pro- 
thallium the cotyledon is more or less strongly bilobed and 
the divisions are also lobed. This is accompanied by a fork- 
ing of the veins, so that in the primary leaf, as well as the 
later ones for some time, the branching of the lamina is 
