112 



MORPHOLOGY 



FIG. 246. Sphag- 

 terminal cluster 



The leaves at first have similar cells, but later there is a striking differentiation, 

 certain of the cells becoming enlarged, hyaline, and perforate (figs. 244, 245). 

 It is this abundance of hyaline cells and paucity of 

 chlorophyll-containing cells that give a pallid look to the 

 leaves. 



The axis of the leafy branch is differentiated into three 

 regions : (i) a cortex of empty and perforate cells, like the 

 hyaline cells of the leaf; (2) a cylinder of elongated cells 

 with thick walls and small caliber (prosenchyma) ; and 

 (3) a pithlike axis. 



There are no special structures for vegetative 

 multiplication, but great masses of individuals are 

 formed by the indefinite growth and branching 

 above, accompanied by dying off below. 



Antheridium. The antheridia occur on special 

 densely leafy branches resembling small catkins 

 (fig. 246). The leaves also usually differ in color 



from the ordinary leaves, and in the axil of each there is a solitary 



globular and long-stalked antheridium (fig. 247), just as in Porella 



(see p. 104). These antheridia 



develop by means of an apical 



cell with two cutting faces, the 



lower segments forming the 



stalk, and the upper segments 



forming the capsule, which is 



initiated by a series of peri- 



clinal walls that cut off the 



peripheral wall layer from a 



central spermatogenous group 



of cells. The antheridium 



opens by irregular lobes and 



discharges the two or three- 



coiled biciliate sperms. 



Archegonium. The arche- FIG. 247. Sphagnum: an antheridium aris- 

 ,, ,. ing on branch between two leaves, showing the 



goma occur at the apex of slender stalk and the g]obular head; the Jatter 



short branches, at the top of consisting of a wall (a single layer of cells) in- 

 the plant (figs. 248, 249). vesting a mass of spermatogenous cells (in 



They are stalked and free, whichbl 



and develop as in the acrogynous Jungermanniales, the archegonium 



initials being segments of the apical cell, which itself finally becomes an 



