MUSCI. 
in the botanical laboratory at Würz burg, and concluded b}^ Müller (1873). The 
principal filaments of the protonema and the large rhizoids have a very much 
elongated apical cell in which (and never in its segments) oblique septa are 
formed which are regularly inclined (spirally) in three or more directions, just in 
the same manner as the principal walls of the segments of the trilateral apical 
cell of the Moss-stem. These walls do not, however, intersect, as in the stem, 
since the segments (cells of the filament) are so long. Each segment is capable 
of forming a protuberance immediately behind its anterior wall, which is shut off 
by a wall corresponding to the 'foliar wall' formed in the stem-segments. After 
this protuberance has become elongated a wall is formed within it corresponding to 
the 'basal wall' formed in the segments of the stem. In this way the protuber- 
ance comes to consist of two cells; the one directed towards the growing apex 
of the filament corresponds to the mother-cell of the leaf, and the other, lying 
behind the preceding, developes a lateral branch, just as is the case in the stem ^ 
Other unimportant divisions of these cells need not be mentioned here. Usually 
Fig. 24R. — Production of rhizoids from the protonema of Milium horniun, with leaf-forming buds A'; 
iu TV the root-hairs of an inverted sod, from which shoot protonema-filaments ti ii (X 90), 
the anterior cell does actually give rise to a foliar organ, the posterior to a bud, 
but often one or both simply develope into rhizoids. The position of the walls 
of these cells is precisely similar to that of the corresponding cells of the stem ; 
the protonema diff'ers from the Moss-stem simply in the distance of one segment 
from the other, and in the suppression of those further divisions by which the 
tissue of the stem is produced from its segments. When a stem is developed 
from the protonema, it originates as a bud from the posterior of the two cells of 
the lateral protuberance. Its mode of origin is usually this, that the cell at first 
elongates into a filament by the formation of segments the primary walls of which 
do not intersect; after this segments are cut off by walls which do intersect, 
and from them foliar outgrowths, and later true leaves, are formed. From this 
it is 'evident that the formation of a Moss-stem from the protonema essentially 
depends upon the more rapid formation of segments one after another ; a Moss- 
stem is, so to speak, a protonemal filament with very short segments, forming 
^ See Fig. ii6, the walls c. b. 
