ERYOPIIYTES 121 



(2) Stegocarpae (or stegocarps), characterized by an operculum and 

 generally a peristome. The stegocarps are much the more numerous 

 and representative mosses, comprising two groups : {a) Pleurocarpae, 

 with the archegonia (and of course the sporophyte) terminal on short 

 lateral branches ; and (b) Acrocarpae, with the archegonia terminal on 

 the main axis. Highest among the stegocarps is the great family Poly- 

 trichaceae, of unusual size and complexity in both leafy branch and 

 sporophyte. The leaves have a specially organized chlorophyll tissue ; 

 the central region of the stem and seta almost suggest conducting tissue ; 

 and there are distinct leaf traces. 



Conclusions. — Some of the general conclusions as to bryophytes 

 may be summarized as follows: The gametophyte begins as a simple 

 thallus body and culminates as a filamentous body bearing erect leafy 

 branches. This is the gametophyte at its best, for in the higher groups 

 it is much less highly developed. Such a gametophyte introduces condi- 

 tions unfavorable for the functioning of sperms. 



The sex organs are fairly constant, the archegonia more so than 

 the antheridia. There is a shifting in position from a general distribu- 

 tion over the dorsal surface of the gametophyte to special regions, 

 and finally to the tips of leafy axes, and in this terminal position the 

 archegonia preceded the antheridia. The conspicuous exception in the 

 development of sex organs and their relation to the gametophyte is 

 found in Anthocerotales, in which they are embedded in the tissue of 

 the thallus, the antheridium developing from the inner cell resulting 

 from the periclinal division of the initial, and the archegonium being 

 invested by the growing tissue of the thallus. This relation of the arche- 

 gonium to the tissue of the thallus is characteristic of pteridophytes. 



The sporophyte begins as a simple spore case, being all sporoge- 

 nous except the single layer of wall cells. But progressive sterilization 

 of potentially sporogenous tissue proceeds through all bryophytes, 

 culminating in the true mosses, in which the sporogenous tissue is 

 much reduced in extent and appears late, and the great bulk of the 

 sporophyte consists of sterile tissue, from which develops a foot, a 

 highly differentiated seta, and a capsule of remarkable complexity. 



The sporophyte is dependent upon the gametophyte in all bryophytes, 

 but there is evidently a tendency towards independence, as shown by 

 the development of chlorophyll tissue, which reaches its highest ex- 

 pression in Anthocerotales and in the apophysis of certain mosses. 



