BRYOPHYTES 



117 



is rare, and in some cases even sex organs are rare. Therefore, it is 

 probable that reproduction is chiefly by vegetative multiplication, which 

 may occur as follows : (i) the isolation of branches by the death of 

 older axes ; (2)- the production of gemmae ; (3) the production of resting 

 buds on the protonema, which seem to be only arrested branch buds 

 (fig. 251) ; and (4) under appropriate conditions, the development of 

 a new protonema from any part of the leafy branch, or from fragments 

 of leaves and axes. It follows that a gametophyte once started may 

 propagate indefinitely. 



Sex organs. The sex organs are grouped at the end of the main 

 stem or of its branches. Around this terminal cluster of sex organs 

 the leaves usually become modified in form and 

 sometimes in color, forming a sheath or a rosette 

 (figs. 252, 253), the whole being the so-called moss 

 " flower," a most inappropriate name. The anther- 

 idia and archegonia may occur together in the same 

 cluster, or they may be in separate clusters, and 

 sometimes they are intermixed with multicellular 

 hairs (paraphyses). 



In the true mosses the antheridia hold the same 

 relation to the apical cell that the archegonia 

 hold in the acrogynous Jungermanniales and in 

 Sphagnales. The antheridium initials are seg- 

 ments of the apical cell, and the apical cell itself 

 usually becomes an initial. The growth is by 

 means of an apical cell with two cutting faces, and 

 the form is usually club-shaped, with a' stalk of 

 variable length. In discharging the sperms, the 

 cells at the apex separate, the mother cells are dis- 

 charged en masse, and then the tip cells spring 

 together again, so that empty but complete anthe- 

 ridia are often observed (fig. 255). 



The archegonia differ from those of the liverworts theridium discharging 

 in one important particular. The central cell (pri- s P erm m ther ^J 



256, a single sperm. 



mary oogenous cell) does not form all of the axial After SACHS. 

 row, which is added to by successive divisions of the 

 cap cell. The mature archegonia of mosses are usually more conspicu- 

 ously stalked than in the other groups, with more massive venter, and 

 with smaller, more numerous, and more ephemeral canal cells (fig. 257). 



255 



FIGS. 255, 256. 

 True moss: 255, an an- 



