1906] LEWIS—DEVELOPMENT OF RICCIA ieiy/ 
In Riccia minima, LINDENBERG (20, p. 429) describes and in 
pl. 20 figures the antheridia as arranged in two rows, one on each 
side of a median groove. In Riccia bulbosa the antheridia are along 
the median groove for its entire length, sometimes in pairs and 
sometimes far apart. Riccia Bischoffit has the antheridia in two 
or three rows in the thallus. 
It seems highly probable that a careful study of a large number 
of species of Riccia by modern methods would show that in many 
of them there are produced groups of antheridia and archegonia 
in distinct parts of the thallus. 
Since the characters upon which the genus Ricciocarpus has 
been based, with the single exception of the structure of the thallus, . 
have been found wanting, it seems to me that there is not sufficient 
reason for retaining the genus. The thallus varies in form according 
to the supply of water, and when growing on the soil has been called 
a species of Riccia. Many plants assume quite different forms 
when growing under different conditions, but the different forms 
are not regarded as species. 
We should then write: 
RICCIA NATANS L. Syst. Veget. 956. 1774.—Bischoff, Nova Acta 
Acad. Caes. Leop. Carol. 17: 2. 1835.—Lindenberg, Nova Acta 
Acad. Caes. Leop. Carol. 18:—1836.—Sullivant, Gray’s Manual 
2ed. 1856. 
Ricciocarpus natans Corda, Opiz Naturalischentausch. 1829.—Leitgeb, Die 
Riccien, Unters. Lebermoose 4:1879.—Lindberg, Revue Bryol. 9:82. 1882. 
(Includes Riccia natans L. and Riccia lutescens Schw.)—Schiffner, Engler and 
Prantl. 1893.—Campbell, Mosses and Ferns. 1895.—Underwood, Systematic 
Botany of North America. Hepaticae. 1895.—Garber, Bot. GAZETTE 3'7:101- 
177. pls. Q-10. 1904. 
Riccia lutescens Schw. Specimen Fl. Amer. Sept. Crypt. 26. 1821.—Linden- 
berg, Nova Acta Acad. Caes. Leop. Carol. 18: pl. 26. 1836.—Sullivant, Mem. 
Amer. Acad. II. 4: fl. 4. 1849.—Sullivant, 2d ed. Gray’s Manual 684. 1856. 
—Underwood, Systematic Botany of North America, Hepaticae. 1895. 
Riccia velutina Hooker (in part) Ic. Pl. pl. 149: founded on sterlile thalli of 
Riccia lutescens and fertile thalli of Riccia crystallina, according to Sullivant, 
Gray’s Manual, 1856. 
EMBRYOLOGY. 
Material for study was collected during the autumn and spring, 
and fixed very satisfactorily in 1 per cent. chromacetic acid or in 
chromosmacetic. 
