The Morphology of Ruppia Maritima. 133 
In his work on Ruppia rostellata (1902, pp. 4 and 5) Murbeck, 
indeed, locates a hypodermal archesporial initial layer, which is 
quite in line with the vast majority of results so far obtained 
among the Angiosperms. These hypodermal cells divide into 
primary parietal and into primary sporogenous cells, which develop 
in the usual way. 
As is evident, Murbeck’s report does not correspond with what 
I have seen in Ruppia maritima. But the statements of Warming 
and Campbell are strong evidence that the state of affairs I have 
described is quite possible. It is well known that Campbell has 
found a plerome origin for the archesporial cells in azas (1897, p. 13) 
and in Lil/aea subulata (1898, p. 8). A careful study of the history 
of the archesporial initials in Ruppia maritima from the meristematic 
stage, as outlined above, leaves no room for doubt that we are here 
dealing with a comparatively large group of cells which originates 
simultaneously both in plerome and periblem. Very probably, as 
Warming’s and Campbell's studies indicate, Zannichellia develops in 
a similar way. The archesporial initials of Lemna minor, as figured 
by Caldwell (1899, figure 13), to whose paper I shall have occasion 
to refer more at length later, closely resemble those of Ruppia 
maritima. On the other hand, Wiegand (1899, p. 344) finds the 
archesporium in Potamogeton traceable to a single hypodermal cell. 
Pl. XI, fig. 69 shows a more advanced stage, the length of the 
young flower (fig. 70), measured as in the preceding case, being about 
0.25 mm. One or two divisions have occurred evidently in all the 
cells. Although the cells representing the parts of the mature 
microsporangium are as yet entirely undifferentiated as to their 
contents, yet the manner of cell-division and the orientation of the 
walls give evidence of a commencement of a differentiation. First, 
the majority of the hypodermal cells have divided by a periclinal 
wall, thus separating off the primary parietal layer. Second, at the 
left of the top of the figure, there is the first indication, by character- 
istic periclinal and anticlinal divisions, of the future septum dividing 
the two sacs of the theca. 
In Pl. XI, fig. 71, with a length of flower about 0.3 mm, this wall of 
separation between the two sacs becomes quite distinct. Its cells 
have a much less dense content than the archesporial cells, and 
are thus clearly marked off from them, as well as by the orientation 
of their walls. 
A parallel case of a wall formed in an exactly similar way has 
recently been found by Caldwell (1899, pp. 47, 48) in Lemna 
minor. Coulter and Chamberlain (1903, pp. 39, 40) in commenting 
