THE CHROMOSOMES OF RICCARDIA PINGUIS 
Amos M. Showalter 
(Received for publication June 20, 1922) 
This study of the chromosomes of Riccardia pinguis (L.) S. F. Gray 
was made with reference primarily to possible sex differences. The material 
used was collected August 11 and 12, 1921, in the swamp prairie bordering 
Lake Waubesa, near Madison, Wisconsin. The methods of fixation, 
staining, etc., have been reported in a previous paper (Showalter, 1923) and 
need not be repeated here. This material was supplemented with green¬ 
house plants grown from Florida and Wisconsin stock. 
My choice of this plant for such a study was due in part to a suggestion 
of Dr. W. N. Steil, who had observed that the male plants are sometimes 
noticeably smaller than the female, but my observations in field and cultures 
have convinced me that there is no marked sexual dimorphism in this species. 
Division figures are fairly frequent in the massive embryonic tissue at 
the growing ends of the thallus and in the young sex organs. The chromo¬ 
somes are relatively large and are easily stained so that they stand out in 
brilliant color contrast to the rest of the cell contents. The spermatogenous 
cells of the antheridium, however, are less favorable for counts of the chromo¬ 
somes because the cells are small (except in very young antheridia) and 
division figures are consequently crowded, so that the chromosomes of one 
cell are not easily distinguished with certainty from those of the adjacent 
cells. 
In the cells of the embryonic tissue of both male and female plants and 
in those of the archegonium, the chromosomes are frequently well spread 
out on the spindle at the equatorial plate stage and in polar view are espe¬ 
cially favorable for study. I have studied a large number of division figures 
in the plants from the region of Madison, and the evidence seems conclusive 
that the haploid number of chromosomes is ten (figs. 1-18, PI. XX). Far¬ 
mer (1905), in studying the reduction divisions, reported casually that the 
number “seems to be eleven for the species in question.” Occasionally 
a small spherical body which stains like a chromosome is found near or 
among the chomosomes (figs. 2, 11, 12). I have not traced the behavior 
of this body, but there is little reason to suspect that it may be chromosomal 
in nature or origin. It may possibly be a fragment or vestige of the nucle¬ 
olus. 
The chromosomes are relatively smooth, rod-shaped structures, fairly 
uniform in thickness and variously bent (figs. 1-19). They differ some¬ 
what in size, but only one, the smallest, is distinguishable with certainty 
in any large number of cases. The chromosomes which appear in sporo- 
170 
