202 Rhodora [DECEMBER 
series of specimens (25 collections) from Willoughby, in all stages of 
development, shows that the young pods are distinctly pubescent 
but in maturity become glabrate, so that at best the Willoughby 
plant is a weak variety. 
Arabidopsis Schur, Enum. Pl. Trans. 55 (1866) which had but a 
single species, A. Thaliana (L.) Schur,! based on Arabis Thaliana L., 
has the same type as Pilosella Kostel. Enum. Hort. Prag. 104 (1844) 
and as Stenophragma Čelak.? and, although Arabidopsis is said to go 
back to DeCandolle’s Sisymbrium, section Arabidopsis, it is note- 
worthy that Schur recognized only the single species A. Thaliana and 
that the latter plant was placed by DeCandolle under Arabis not under 
Sisymbrium, sect. Arabidopsis. 
Whether or not Pilosella Kostel. (Arabidopsis Schur or Stenophragma 
Čelak.) is treated as a distinct genus or as a subgenus of Sisymbrium, 
its status as a genus or as a subgenus is at once invalidated by thrust- 
ing into it species of Braya Sternb. & Hoppe, Regensb. Denkschr. 
i. pt. 1, 65 (1815). And surely no one who will take the time and 
trouble to examine with moderate power the septum of Pilosella 
novae-angliae Rydb. or Arabidopsis novae-angliae Britton can doubt 
that this plant is a Braya. The fact that the Willoughby and Anti- 
costi plant has the septum of Braya and not of Sisymbrium and Arabi- 
dopsis or Stenophragma has already been pointed out by Robinson.’ 
Microscopic examination of the septa of many specimens, from New- 
foundland, Anticosti, Willoughby, Keewatin, British Columbia and 
Siberia of Braya humilis; of the northwestern species labeled in 
Rydbergs own hand Pilosella Richardsonii Rydb.; of the Arctic 
B. purpurascens (R. Br.) Bunge; of the European B. alpina Sternb. 
& Hoppe, and of several other boreal species, shows clearly that 
these plants all have the characteristic septum of Braya, with the 
thick-walled cells elongated transversely. Furthermore, the starved 
and dwarfed material of Braya humilis (the American specimens of 
which are included by Britton in Arabidopsis novae-angliae) from 
i This appears in the Illustrated Flora, ed. 2, as Arabidopsis Thaliana (L.) Britton, but 
Schur published the name in 1866 when he published the genus. 
2 Index Kewensis cites Slenophragma Celak. as published in Arch. Naturw. Landesd. Boehm. 
iii, 445 (1875); Britton starts it in Flora, lv. 438 (1872), but in the latter very critical discussion 
of the characters of the genus Celakovsky himself states that the genus, based on Arabis Thali- 
ana, was published by him in his Flora der Prager Umgegend (1870), a work to which the 
present writec has been unable to refer. 
3 Robinson in Gray, Syn. Fl. i. pt. 1, 141 (1895). 
