The Morphology of Riccia Frostii, Aust. 
BY 
CAROLINE A. BLACK. 
With Plates XXXVII and XXXVIII. 
General Characters. 
HE summer and autumn of 1908 were characterized by an exceedingly 
-L long drought in Bloomington, Indiana. During the autumn, as the water 
in the reservoir which supplied the town gradually diminished, the basin of 
the reservoir was covered with patches of Riccia Frostii , Aust. 1 The ground 
in its moist condition, roughened by cracks as a crust gradually formed, 
provided an ideal habitat for the Liverwort, as evidenced by its luxuriant 
growth. Tracks made by workmen, horses, &c., furnished further protection 
and conservation of water, and on the border of these the plants were also 
numerous. The Liverwort was found in patches several metres square, or 
in solitary rosettes, and in colour appeared dull green to reddish. The 
following years, 1909-10 and 1910-11, although dry, never exhausted the 
water in the reservoir. Comparatively little Riccia was found, and this 
only on the banks of the reservoir. Riccia Frostii was described as a new 
species by C. F. Austin ( 2 ) in 1875. Underwood ( 42 ) includes Riccia Frostii 
in his Hepaticae, and describes it fully. 
Riccia Frostii, Aust., when grown uncrowded develops a thallus, in form 
a typical rosette, varying in diameter from 5 to 1 2 mm., attached to the ground 
by simple rhizoids. Young plants are irregularly and more deeply lobed than 
older, fully developed ones. This is well shown in PI. XXXVII, Figs. 1-5, 
which are photographs of plants, enlarged four times. The central portion 
sometimes decays as the plant grows, and results in unsymmetrical rosettes. 
There is present a dichotomous branching which gives rise to a circular 
plant, with a number of growing points situated in depressions at the edge 
of the rosette (Figs. 1 and 2). As a whole the thallus is compact (Figs. 1 
and 2). When the plants are found growing under crowded conditions, the 
typical rosette form is lost in the overlapping of the different plants, which 
pile up and grow irregularly as they encroach upon each other. The 
1 Acknowledgement is due to Mr. Marshall A. Howe, who kindly determined the species as 
Riccia Frostii , Aust. 
[Annals of Botany, Vol. XXVII. No. CVII. July, 1913.] 
