138 A. H. Graves, 
glance might have interpreted as three megaspores, the upper two 
becoming resorbed. But careful focussing discloses another outer 
cell at a somewhat lower plane. Murbeck (1902) figures a similar 
case in Ruppia rostellata. 
This departure from the usual method of division of the mega- 
spore mother-cell, in which, in general, the resulting cells are 
formed in a straight row, is fully commented upon by Murbeck 
(1902, p. 13), who states that it has been found also in A/honia 
nyctaginea, Helleborus foetidus and Ceratophyllum demersum; and 
to his work I refer for a fuller account of the whole matter and 
for literature bearing upon the subject. A concise morphological 
consideration of such a location of the potential megaspores is also 
set forth by Coulter and Chamberlain (1903), who although they 
do not mention the case of Ruppia rostellata, note a similar arrange- 
ment of the outer two cells as occurring in Butomus (Ward, 1880), 
Jeffersonia (Andrews, 1895), and Potamogeton (Holferty, 1901). 
Moreover, that this position of megaspores is not an invariable 
rule in Ruppia maritima, is shown by such a case as 1s illustrated 
by Pl. XII, fig. 81, where the four cells appear in a row, the two 
outer ones already much disorganized. 
Before proceeding further, the condition shown in Pl. XII, fig. 82 
should be noted, where the nucleus of the upper of the two daughter- 
cells has divided, but no wall has been formed, and the whole cell, 
along with its neighbor below, is undergoing resorption. Such a 
happening seems natural when one reflects that the division in the 
lower daughter-cell in general precedes that in the upper cell, 
producing a tendency by the earlier development of the former, 
to reduce activity in the upper daughter-cell. It will be seen later 
that this omission of the wall in the upper daughter-cell is the 
ordinary occurrence in Potamogeton foliosus. 
In all cases the lowest of these four cells becomes the functional 
megaspore, the upper three cells becoming resorbed, as in Ruppia 
rostellata (Murbeck, 1902, pp. 14, 15). 
In Potamogeton natans, Holferty (1901) describes cases of four 
megaspores with the same arrangement as in Ruppia, the innermost 
functioning. 
In Potamogeton foliosus, described by Wiegand (1900), the con- 
dition is quite different and yet exhibits points of similarity. The 
first reduction division produces two daughter-cells, separated 
by a wall. The second division then takes place in each of these 
cells, and the resulting nuclei occupy practically the same positions 
as‘ they do in Ruppia. No walls are formed after this division, 
