212 STRUCTURE AND LIFE HISTORIES 
ANTHOCEROS 
194. The Gametophyte. One of the most important 
groups is the genus Anthoceros, including several different 
kinds or species. The plant body, or thallus (Fig. 156), is 
roughly circular or semicircular, with numerous rhizoids 
growing from the ventral surface. It increases in size at 
numerous growing points on the margin of the thallus, and 
FIG. 155. A leafy liverwort (Porella navicularis). Female plant, about 
natural size. (After M. A. Howe.) 
is green from the presence of chlorophyll in the cells. 
There is only one chloroplast in a cell, in contrast to the 
numerous chloroplasts in each cell of the mosses and ferns. 
195. Reproductive Organs. The antheridia are found 
just back of the growing points, near the middle of the 
lobe. In some species they occur in groups (Figs. 157 
and 1 59) , in other species singly (Fig. 158) . They develop. 
