162 BOTANICAL GAZETTE [MARCH 
growth, the formation of air chambers and pores, and showed 
that the ventral scales are homologous with the walls separating 
the air chambers. Corda had previously suggested the separa- 
tion of Ricctocarpus natans from Riccia as an independent genus. 
Leitgeb, after examining Ricciocarpus, gives the following as 
distinguishing characters: (1) the constant presence of definitely 
formed air pores similar to those of Corsinia and Boschia; (2) 
numerous ventral scales which are formed independently and 
have long-continued basal growth; (3) a rudimentary integu- 
ment ( Hiille) around the sporogonium ; (4) antheridia collected 
into groups similar to those of Marchantiaceae. Leitgeb lays 
stress on the grouping of sex organs, and suggests a progressive 
series in which the lowest member has the sex organs scattered 
indiscriminately over the upper surface and the highest has the. 
definite group of sex organs terminating a branch. 
Fellner (14) studied the germination of the spore and the 
development of the thallus in Riccia glauca. 
MATERIAL AND METHODS, 
The material for the present study was collected during the 
spring and summer of 1902, and was fixed in a chrom-acetic 
acid mixture (1 per cent. of each) for twelve to twenty-four 
hours. After washing thoroughly in running water for a few 
hours, the plants were brought gradually into 70 per cent. alcohol. 
Pieces including an apex of a branch and a dorsal furrow were 
cut from these preserved plants. Since the loose, delicate tissues 
are very likely to collapse, the material should be hardened and 
dehydrated gradually, and the absolute alcohol should be 
renewed once or twice to insure perfect dehydration before any 
xylol is added. It is well to have xylol grades of 25, 59; and 
75 per cent. in absolute alcohol, through which the material 1s 
passed with intervals of an hour between successive grades. 
After a short time in pure xylol, paraffin is added as fast as it 1S 
dissolved by the xylol. The paraffin should be changed three oF 
four times during the three hours in the bath, after which the 
material may be imbedded. Sections perpendicular to the flat 
surface of the thallus and also to the median furrow are best for 
