The Morphology of Ruppia Maritima. 149 
a four-celled embryo is formed from the first embryo-cell by two 
longitudinal divisions occurring at right angles to each other, and 
these quadrant-like cells are next each divided by a transverse wall. 
So that, although the divisions here occur in different sequence, 
the two four-celled segments nevertheless result. 
Although these first stages were not followed out by Rosenberg, 
he presents a figure (1901, I, Pl. I, fig. 20, and P. 12) of an eight- 
celled embryo similar to that of Wille’s (Pl. XIII, fig. 99). It is 
perhaps possible that later investigation will show that the first wall 
in Zostera is transverse instead of longitudinal, as Hofmeister has 
described it. 
The task of tracing out the lines of demarcation of the primary 
segments during the later stages, after the manner of recent embryo- 
logical investigations, is very difficult, probably from two principal 
causes. First, the remarkable number of early longitudinal divisions 
which have already been indicated to a certain extent obscure the 
segment limits. Second, the form of the mature embryo differs so 
widely from that of a typical monocotyledon that even in the early 
developmental stages this influence makes itself felt, and renders 
comparison with type forms rather unsatisfactory. Wille, indeed 
(1883, pp. 2, 3), describes his eight-celled stage as forming a 
sixteen celled structure by transverse divisions in all of the eight 
cells. But of the subsequent divisions he says (I. c., p. 3), ‘ Herefter 
gaa Delingerne uregelmessigt, saa man ikke lengere med Be- 
stemthed kan felge de enkelte Cellers Delinger.” 
Of stages older than the eight-celled embryo of Wille and Hof- 
meister, | was fortunate in having a fairly large number, and in 
the following description I shall attempt to show to what extent 
the segment boundaries may be traced during the embryo develop- 
ment, and how they may be correlated to such a type as Sagit- 
taria. 
I have already suggested that such an embryo as is represented 
in Pl. XIII, fig. 100, composed of twelve cells, or three four-celled 
segments, arises from Wille’s younger form by a transverse wall 
through one of the segments, and that this is parallel to the case in 
Sagittaria, where a three-celled row arises by a transverse division 
in the lower embryo-cell. 
Fig. 101 is a slightly older embryo, in which the divisions are 
somewhat irregular, but still admit of an interpretation which reveals 
the outlines of the cells and segments in the preceding stage. It 
is evident that a transverse division has occurred in the terminal 
Segment. 
