Apr., 1923] SHOWALTER — CHROMOSOMES OF RICCARDIA 171 
phytic divisions have the same general appearance as have those seen in 
the thallus, though, of course, in the double number (fig. 19). 
I have not studied exhaustively the chromosomes of the plants received 
from Florida, but the few dozen division figures examined have convinced 
me that the number and relative sizes of the chromosomes are the same as 
those of plants from the vicinity of Madison (figs. 20-24). In two or three 
division figures from the Florida plants there appear to be eleven chromosomes 
(fig. 21), but this appearance may be due to a part of one chromosome having 
been displaced by the microtome knife. 
Previous investigators of the morphology of this species agree that it is 
strictly dioecious, but this conclusion seems to be based upon field observa¬ 
tions and not, so far as I have been able to find, upon conclusive cultural 
experiments. My own attempts to grow the plant in culture have not been 
highly successful and have yielded no conclusive evidence, but in all cases 
observed, both in cultures and in the field, the male and female sex organs 
were produced on separate plants. 
The comparative study of the chromosomes of the two sexes, as in the 
case of my earlier study of the chromosomes of Conocephalum (Showalter, 
1921), has revealed no perceptible difference between the sexes. Exact 
micrometric measurements of the chromosomes have not been made, but 
the camera lucida drawings show no perceptible difference between the 
chromosomes of the male and those of the female plants ^figs. 1-18). The 
evidence seems conclusive that there is in this species no such chromosome 
difference between the sexes as is found in Sphaerocarpos (Allen, 1917, 1919; 
Schacke, 1919). 
I wish to express my gratitude to Professor C. E. Allen, under whose 
direction this study was made. 
Department of Botany, 
University of Wisconsin 
LITERATURE CITED 
Allen, C. E. 1917. A chromosome difference correlated with sex differences in Sphaero¬ 
carpos. Science, n. ser. 46: 466, 467. 
-1919* The basis of sex inheritance in Sphaerocarpos. Proc. Amer. Phil. Soc. 58: 
289-316. 
Farmer, J. B. 1905. On the maiotic phase (reduction divisions) in animals and plants. 
Quart. Jour. Microsc. Sci. 48: 489-557. 
Schacke, Martha A. 1919. A chromosome difference between the sexes of Sphaerocarpos 
texanus . Science, n. ser. 49: 218, 219. 
Showalter, A. M. 1921. Chromosomes of Conocephalum conicum. Bot. Gaz. 72: 245- 
249. 
-1923. Studies in the morphology of Riccardia pinguis. Amer. Jour. Bot. 10: 148-166. 
EXPLANATION OF PLATE XX 
All figures were drawn with the aid of an Abbe camera lucida, using a Zeiss 2-mm. 
apochromatic objective N. A. 1.40, and compensating ocular 18, at a magnification of about 
4,000 diameters; reduced in reproduction to about 2,650. 
