MUSCI. 



3^^ 



in the botanical laboratory at Wurzburg, and concluded b}^ MuUer (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. 248.— Production of rhizoids from the protonema oi Mnium hornunt, with leaf-forming buds K ; 

 ■w TV the root-hairs of an inverted sod, from which shoot protonema-filaments « « (X go), 



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 differs 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. 116, the walls c, h. 



