512 Black . — The Morphology of Riccia Frostii , Aust. 
surface of the thallus Is characterized by minute depressions or pits corre- 
sponding to the air-spaces beneath. Underwood describes the thallus of 
Riccia Frostii as probably dioecious. It was found to be strictly dioecious. 
It begins to fruit when very young, and a succession of sexual organs is 
maintained as the thallus develops. Plants only 3 or 4 mm. in diameter 
were found with mature sporophytes. The globular sporophytes were seen 
readily with the naked eye, the older ones appearing black. 
The abundance of material found in all stages of development, together 
with the interest in recent years in various phases of the life-history of 
different Liverworts, suggested the desirability of making a study of this 
plant. Material was fixed in chromacetic acid, and in the chrom-osmic- 
acetic acid mixture prepared according to the formula of Mottier ( 36 ), 
washed, dehydrated, and embedded in paraffin. Sections were cut from 
2 to 7 fj., the majority being 2 /x thick. A number of different stains were 
used. Satisfactory results were obtained with anilin, safranin, and gentian 
violet, with or without the orange G, with Heidenhain’s iron-alum-haema- 
toxylin, and with Bismarck brown and gentian violet. 
Bischoff (8) in 1835 described and figured a number of species of 
Riccia , emphasizing the method of reproduction, and proposing the terms 
4 antheridia * and ‘ archegonia ’ for the male and female organs respectively. 
In 1836 a monograph on the Ricciaceae by Lindenberg ( 33 ) appeared. The 
earliest detailed account of the morphology of Riccia is by Hofmeister ( 25 ), 
who described the development of the thallus, the origin and position of 
the archegonia and antheridia, and the formation of the sporophyte. He 
remarks that the earlier investigators have described exclusively the organs 
of fructification, assuming that ‘the low state of development of fruit must 
be accompanied by an equally low state of development of the vegetative 
organs k 1 Kny ( 30 ) investigated the structure of the thallus of various 
Ricciaceae and established its development by means of apical growth, 
showing the origin of the ventral scales, the sexual organs, and the nature of 
the air cavities. Fellner ( 20 ) is the first to record the development of 
a thallus of Riccia glauca from the spore. In a complete investigation by 
Leitgeb ( 32 ) of the following species of Riccia , R. glauca , R. bifurcata , 
R. crystallina , R.fluitans , R. Bischoffii , and Ricciocarpus natans } the develop- 
ment of the thallus and the origin and nature of the air-spaces are minutely 
described, together with some phases of the reproductive organs and 
sporophyte. 
Structure of the Thallus. 
The development of the thallus of R. Frostii , Aust., is in the main in 
accordance with that of other Ricciaceae as outlined by Campbell ( 9 , p. 24). 
Growth takes place from one or more apical cells situated in a depression 
1 Hofmeister: On the Higher Cryptogamia, p. 97. 
