148 A. H. Graves, 
monocotyledonous embryo (Coulter and Chamberlain, 1903, pp. 188, 
190 ff.). 
Instead of the increase of this row of cells from three to four, 
or, in other words, to a row of three embryo-cells, as is the case 
in the above-mentioned genera, Wille, as already stated, finds that 
two plates of four cells each are formed from the two embryo-cells. 
These two resulting four-celled segments are, nevertheless, still the 
representatives of the two small embryo-cells, which are formed 
first, in Ruppia as well as in Sagittaria and Alisma. 
That this condition is the usual one in Ruppia is shown not only 
by Wille’s (1883) observations, which may be correlated so well 
with my own, but also by the figures and description of Hofmeister 
(1852, p. 143 and figures 41-46, and 1861, figures 1—7, pl. ID). 
My twelve-celled embryo (Pl. XIII, fig. 100), composed of three 
four-celled plates, has obviously arisen by a transverse wall through 
one of these four-celled segments—which one, it is not possible to 
state. In the typical embryo of Sagittaria, indeed, it is the lower 
of the two segments that undergoes a transverse division (Schaffner, 
1897. II, p.262 and Pl. XXIV, figures 46, 48, 49), and this may be 
the case here. 3 
What has occurred then is simply the formation of three seg- 
ments, one above the other, comparable to the three upper cells in 
Sagittaria (Schaffner, 1897, H, Pl. XXIV, figures 48, 49), with the 
difference that in Ruppia longitudinal divisions precede the trans- 
verse ones. 
A comparison of this stage with those embryos of related genera 
which have been worked out, brings to light the following points. 
The embryos of Zannichellia (Campbell, 1897, p. 48 and cf. fig. 63 
Pl. UI; Hofmeister, 1861, Pl. I, fig. 18) and Potamogeton (Wiegand, 
1900, pp. 37, 38, and Pl. VII, figures 25, &c.) are essentially like 
that of the typical Sagittaria, consisting of a row of three cells 
above the suspensor-cell, the terminal one being the first to undergo 
longitudinal divisions. 
As to the embryo of Zostera, it was investigated at a very early 
period by Hofmeister (1852), and quite recently by Rosenberg 
(1901, I). Their results are not complete in the early stages, but 
enough has been shown to indicate that Zostera is more like Ruppia 
in the early development of its embryo than any of the Potamo- 
getonaceae so far investigated. Hofmeister (1852, p. 139) states that 

' Practically the same figures are presented in each of these articles: 
in the former, the species is given as rosted/ata, in the latter, as maritima. 
