1898] REGENERATION AS EXHIBITED BY MOSSES 173 
I. MNIUM ROSTRATUM. 
On account of the size of its leaves and the consequent ease 
of manipulation Mnium presents a very favorable specimen for 
experimentation. In its power and manner of regeneration it 
stands alone among all of the species investigated. At first two 
cultures were made for exposure to light; the leaves were carefully 
stripped from the stems and in one case placed with the dorsal 
surface uppermost, in the other with the ventral surface upper- 
most. These cultures were placed upona table in the middle of 
the laboratory. Two similar preparations were made and enclosed 
in a dark chamber. 
After an interval of a week the first appearance of rhizoids 
from the leaves was noted. An examination of the specimens 
grown in the light showed that the rhizoids proceeded almost 
exclusively from the contact surface, and in general from the 
periphery of the leaf, although they were not entirely absent 
from the middle and costal region. An examination of the 
cultures in the dark showed nearly the same manner of growth 
except that a considerably larger number of rhizoids originated 
from the side uppermost, the proportion being about one to ten. 
The rhizoids from the very first, both in light and dark, were 
devoid of chlorophyll and the cell walls were distinctly brown. 
As growth proceeded, those in the light developed an abundance 
of chlorophyll bodies and showed in nearly every case oblique 
cross walls. In the course of two weeks the rhizoids in the light 
had branched considerably, while in the cultures in the dark 
they rarely branched, and the cells were more elongated. At 
the end of three weeks the first appearance of buds was noted ; 
and in cultures in brighter light in the window after a lapse 
of two weeks. The buds originated exclusively from the 
illuminated side and directly from a leaf cell without the inter- 
vention of any protonemata. The buds generally made their 
appearance near the periphery of the leaf, and the cell from 
which the bud originated had previously given rise to a rhizoid 
from the contact side. This is shown in cross sections of the 
leaf in figs. 2 and 3. The mother cell of the bud first produces 
