154 A. H. Graves, 
The mature embryos of Ruppia maritima measure 1.5—2 mm. in 
length, by a little more than 1 mm. in width. Although I find no 
measurements recorded of the embryos of FR. roste/lata, Irmisch’s 
figure (1858, fig. 37, Taf. I) is somewhat longer in proportion to 
its width, 
Murbeck (1902, p. 18 and PI. III, figs. 62, 64, and 65) has called 
attention to the resemblance of this curious embryo of Ruppia to 
those of the related genera, Zannichellia, Halophila and Zostera. 
The embryo of Phyllospadix is similar, but characterized by a 
peculiar lobing of the hypocotyl around the base of the cotyledon 
(Dudley 1893, p. 443 and PL. II, fig. H). 
To the well known controversy regarding the real nature of the 
adventitious root and of the primary root, I will briefly allude and 
record my own views here. 
In writing of the Potamogetonaceae, Ascherson (1889, p. 200) 
says, “Meist entwickelt sich eine kraftige Hauptwurzel an dem 
unteren Ende des Embryos; nur bei Ruppia befindet sich dieselbe 
seitlich neben der Plumula.” 
Thus Ascherson, whose view has been adopted by Goebel (1898, 
pp. 464-466), rejects the conclusions of Wille, who found the 
peculiar cell-group developed in &. rostellata, which I have also 
reported for A. maritima, at the base of the hypocotyl and im- 
mediately over the large suspensor-cell. This basal region is, as 
Wille says, the place for the primary root of the embryo. Wille, 
therefore, considers this the rudiment of the primary root, and the 
structure near the base of the plumule, which Ascherson calls the 
primary root, he terms an adventitious root. 
Murbeck agrees with Wille and in further investigations finds 
that the primary root rudiment “sich eben am Festpunkte des 
Embryos, mit anderen Worten, eben am Platze der Radicula be- 
findet. Dass dieselbe wirklich die Anlage der Radicula reprdsentiert, 
kann wohl schwerlich bezweifelt werden” (1902, p. 17). 
That the adventitious root is of exogenous origin is explained 
by Wille (1883, p. 5) and defended by Murbeck (l.c. p. 18) by the 
fact that practically all of the cells of the young embryo are mer- 
istematic, so that an adventitious root developing at this period may 
easily have an exogenous origin. 
My own slides testify to the correctness of the interpretations and 
figures of Wille and Murbeck. Nowhere is there the least evidence 
that the hypocotyl is the “seitliche Auftreibung” described by 
Ascherson, and there seems no doubt but that the root near the 
base of the epicotyl is properly the first adventitious root, which 
