154 A. H. Graves, 



The mature embryos of Ruppia maritima measure 1.5—2 mm. in 

 length, by a httle more than 1 mm. in width. Although I find no 

 measurements recorded of the embryos of R. rostellata, Irmisch's 

 figure (1858, fig. 37, Taf. I) is 'somewhat longer in proportion to 

 its width. 



Murbeck (1902, p. 18 and PI. Ill, 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. 413 and PI. II, fig. H). 



To the well known controversy regarding the real nature of the 

 adventitious root and of the primar}' 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 b}' Goebel (1898, 

 pp. 464—466), rejects the conclusions of Wille, who found the 

 peculiar cell-group developed in R. rostellata, which I have also 

 reported for R. maritima, at the base of the hypocotyl and im- 

 mediatel}' 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 reprasentiert, 

 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 (1. 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 Murljeck. 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 epicot}*! is properly the first adventitious root, which 



