1898 | REGENERATION AS EXHIBITED BY MOSSES 193 
7. POLYTRICHUM COMMUNE. 
Cultures of leaves were made the same as for Atrichum, but 
it was not till the end of about six weeks that the growth of 
protonemata was observed. The protonemata were similar in | 
nature to those already described for Atrichum, with colorless 
walls and oblique cross-walls in both light and dark. A peculiar 
aggregation of branches occurred quite frequently, an example 
of which is shown in fig. 36, thus forming an assimilating organ, 
while the production of buds came later. In the protonemata 
grown in the dark the cells were longer, without chlorophyll, 
and the branching was more or less suppressed. 
The protonemata originated exclusively from the ventral 
surface of the leaf, that is the lamellate side, without reference 
to the position which the leaves occupied in culture. An exam- 
ination of the leaves showed that they came apparently from 
between the lamelle, but the exact origin could only be deter- 
mined by means of cross sections. The sections showed that 
the protonemata originated from the large cells lying just at 
the base of the lamelle (fig. 34). The protonema production 
did not seem to be confined to any particular portion of the 
leaf, but was quite generally distributed over the leaf cells 
occupying the position above named. The portion of the 
lamina not covered by lamellz is small, but the cells from that 
portion of the leaf as well as the cells of the lamella were not 
able to grow out into protonemata.  ~ 
The first production of buds was noted at the end of about 
seven weeks, and, just as in Atrichum, in as great abundance in 
darkness as in light. The buds originated either as modifica- 
tions of lateral protonemal branches or in a few cases by the 
divisions of the end cell of a main protonemal axis. The 
explanation for the production of buds in darkness, here as in 
Atrichum, is to be sought presumably in the nature of the 
leaf, the accessible supply of nutritive material being consider- 
able. 
The complete separation of the leaf from the stem was 
necessary to call forth the protonema formation. The experi- 
