124 MCALLISTER: MORPHOLOGY OF —THALLOCARPUS 
The monoecious plants which Stephani believed he had found 
may possibly be explained on the ground of the small size of the 
male plants and the crowded growth of the thalli, which become 
attached in masses by the rhizoids. The male plants cease growing 
early and are often entirely overgrown by the female plants. In 
dry material it would be difficult to separate the plants or even to 
identify any organic separation. This is often difficult in living 
material collected early in the season. Two cases of what seemed 
at first to be monoecious plants in paraffin sections turned out to 
be distinct plants, the male plant being entirely covered by the 
female plant. There seems little doubt that the Texas Thallo- 
carpus, at least, is dioecious. 
SUMMARY 
1. Thallocarpus, as it occurs in the vicinity of Austin, Texas, 
seems to be strictly dioecious. 
2. The spores of the tetrad adhere after shedding and give upon 
germination two male and two female plants. 
3. The structure of the thallus and the sporophyte is identical 
with that of the Riccias with the exception of the adhering spore 
tetrads and the pegless rhizoids. 
4. The above mentioned structural differences seem insufficient 
to exclude Thallocarpus from the Marchantiales. 
I am indebted to Mr. F. C. Werkenthin, of State College, New 
Mexico, for valuable aid in preparing sections for this study. 
UNIVERSITY oF TEXAS, 
AUSTIN, TEXAS 
