1904 ] GARBER; RICCIOCARPUS NATANS 173 
so that countless numbers may extend over acres of water sur- 
face when the pond freezes. Large numbers of these plants 
probably die, but many of them, as the light and heat diminish, 
gradually become accustomed to submergence. The cold 
weather finally causes the plants to become black and appar- 
ently dead, in which condition they may float, become partially 
submerged, or even sink to the bottom. In this hibernating 
condition the plants have been taken from beneath the ice in 
early spring. When brought to the laboratory, the extreme 
apical region of each dorsal furrow grew out into a new plant. 
These new plants soon assume the vegetative water form and 
separate themselves from the old plant. Bischoff (13) mentions 
that R. natans lives over winter in a similar manner in Europe. 
Rhizoids should be regarded as structures called forth by soil 
life, but in no sense as taking the place of ventral plates, which 
are always present. 
The older parts of the plant possess no plasticity, but the meri- 
stematic region about the apical cell has a plasticity practically 
unlimited. If the plants are very much crowded, so that some 
are forced below the surface of the water, very commonly one or 
more of the apical cells will produce slender branches, which 
grow immediately to the surface. This is evidently an adapta- 
tion to get the plant into a favorable position again with the least 
possible expenditure of energy and tissue. A similar result 
occurred with some plants that were being kept in the laboratory. 
An insect ate out most of the vegetative tissues about the apex, 
and the restraining pressure being removed from them the apical 
cells grew out into independent branches (fig. z, a, c). The 
great plasticity of the apical region in Ricciocarpus gives it 
the possibilities that one would expect to find in a transition 
form from aquatic to terrestrial liverworts. The gametophyte 
on the soil has the essential characteristics of terrestrial forms 
like Marchantia, except that it has not yet acquired the power to 
produce sexually there. If Ricciocarpus should acquire the 
power to produce sexually while on the land, it would become 
independent of the water. 
A fungus belonging to the Ustilagineae frequently attacks the 
