The Morphology of Ruppia Maritima. 133 



In his work on Ruppia rostellaia (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 Naias (1897, p. 13) 

 and in Lilaea 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. 



PI. 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 entirety 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 majorit}' 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 



i 



