200 



PLANT MORPHOLOGY 



Sex Organs. In many mosses sex organs are rarely produced, repro- 

 duction taking place chiefly by vegetative means. The sex organs occur 

 in terminal groups (Fig. 163). In the "acrocarpous" forms they are 

 borne at the apex of the main stem or its principal branches; in the 

 "pleurocarpous" forms they occur at the apices of short lateral branches. 

 The sex organs are usually surrounded by a sheath or rosette of modified 

 leaves forming the perichaetium. According to the species, mosses may be 



Fig. 163. Leafy shoots of Funaria hygrometrica, X 3. A, male plant with terminal cluster 

 of antheridia; B, female plant with an archegonium in which an embryo sporophyte has 

 started to develop; C, older stage, the sporophyte elongating and carrying the calyptra 

 upward. 



either monoecious or dioecious. If monoecious, the antheridia and arche- 

 gonia usually occur in the same cluster. Multicellular paraphyses are 

 commonly present. Both kinds of sex organs arise from segments of the 

 apical cell, in many cases from the apical cell itself. The formation of 

 sex organs limits growth of the vegetative axis. 



The antheridium arises from a superficial cell that becomes papillate. 

 Several transverse divisions may take place and then the terminal cell 

 becomes a dolabrate apical cell (one with two cutting faces), cutting off 

 a series of segments (Fig. 164A). Periclinal walls in the younger seg- 

 ments delimit the jacket cells from the primary spermatogenous cells 

 (Fig. 1645, C). As additional divisions occur, the antheridium becomes 

 club-shaped, with a stalk of variable length (Fig. 164D). A large num- 

 ber of sperm mother cells are formed, each giving rise to two sperms. 



