112 BOTANICAL GAZETTE [FEBRUARY 
produced antheridia, and all stages are found by May 1. About — 
this time fertilization takes place, and by May 25 all stages of sporo- 
phyte are found. The arrangement of the sexual organs in the 
thallus is shown by figs. 7-11. 
The vegetative growth is very rapid during April and May, the 
thallus becoming broad and branched by the increase in the number 
of growing points. The narrow older part by which the thallus is 
attached decays, and the younger part bearing the sexual organs 
and sporophytes is set free and floats upon the water. When the 
plants are supplied with a large amount of water changes take 
place in the lamellae. They grow to great size and become purple. 
In the floating thallus decay of the older part continues; the part 
bearing the antheridia first disappears, then the part bearing the 
sporophytes, and finally the growing points may be separated, one 
thallus thus giving rise to several new individuals. In most cases 
observed the decay of the older parts in floating plants did not advance 
so far. The plants were carried up around the edge of the pond 
by the waves, and as the water went down were left stranded upon 
the mud. When the thalli settle down upon the mud, the large 
ventral plates wither, and rhizoids are put forth which in a few 
days attach the thallus to the soil. Growth now continues at the 
growing points, so that new branches are produced which form 
rosettes. 
When the thallus is injured at this time new plants are imme- 
diately produced from the cells of the apical region. This was 
first observed in plants injured by being covered with mud, in which 
case slender delicate outgrowths were produced (fig. 4). Other 
plants injured by snails soon developed long slender plants (fig. 3b). 
Thalli were cut into pieces to determine whether other cells would 
show the same plasticity, but new plants were produced only from 
cells near the growing point. V6OcHTING (33) found in Lunularia 
that regeneration takes place from cells in various parts of the thallus, 
but this does not seem to be true of Riccia natans under the conditions 
in which I have studied it. Large numbers of the plants which 
were left upon the mud when the water went down were injured 
by cattle coming down to the ponds to drink. Later in the season 
the cattle tracks were lined with young, green, ribbon-shaped plants 
