1898 ] REGENERATION AS EXHIBITED BY MOSSES 203 
produced. At 32°, however, the leaves were killed. At 27° a 
slight growth resulted but with a very marked retardation. At 
24° the growth was to all appearance quite normal. 
That moss plants are able to be dried completely for some 
length of time and still retain their power of regeneration has 
been demonstrated by Schréder.*? By way of confirmation 
Bryum capillare was dried thoroughly for three weeks, then 
moistened and the leaves stripped from the stems and placed in 
conditions favorable for development. In the same time as 
usual protonemata made their appearance. Barbula muralis was 
dried for two weeks without the loss of protonema production. 
The foregoing experiments have shown that in nearly all 
conditions, the only requisite for the development of protonemata 
from rhizoids has been the exposure to light. Either the main 
rhizoid axis has given rise to side branches which were dis- 
tinctly protonemal in nature, or the continuation of the main axis 
has become decidedly protonema-like. There may, however, be 
conditions in which the rhizoids, even though exposed to light, 
do not produce protonemal branches. The rhizoids from Mnium 
leaves, in case the normal development of buds is allowed to be 
carried out, produce no protonemal branches. In the same way 
the rhizoids from the stem did not give rise to protonemal 
branches, but if the growth of the stem is interrupted the rhi- 
zoids undertake the regeneration of the plant and produce new 
leafy shoots and protonemal branches. This manner of growth 
is quite common when tufts of various plants are inverted so 
that the rhizoids are exposed to the light and the shoots killed 
by being covered with soil. 
The experiments which I have carried out show that the 
protonemata do not produce rhizoids with as great readiness as 
the rhizoids do protonemata. This is in opposition to the view 
expressed by Frank,®*since he says in regard to the protonemata : 
“Eben so leicht kann der Faden wieder in ein Rhizoid sich 
umwandeln.” <A protonema of Bryum capillare was grown ona 
* Untersuch, aus d. bot. Inst. zu Tiibingen 2: 15-21. 1886. 
® Lehrbuch der Botanik 2:9. 1893. 
