io6 Alexander W. Evans, 



inflorescences. The sexual branches resemble the vegetative in 

 being constantly lateral in position. In most cases the inflorescence 

 is terminal and occupies the v^hole or nearly the whole of the 

 branch, vv^ithout of course involving the actual apical cell. Some- 

 times, however, the branch shows a sterile base, resembling an 

 ordinary vegetative branch, and sometimes it continues its growth 

 beyond the inflorescence in the form of a proliferation. The 

 proliferation may be short and simple or may, at the other extreme, 

 form a highly complicated branch-system. In such cases the 

 inflorescence may come to occupy a distinctly lateral position on the 

 branch, this being particularly true of female inflorescences. The 

 sexual organs are borne on the dorsal surface and arise in strict 

 acropetal succession, one being formed by each segment cut off 

 from the apical cell. In this way the organs come to be situated 

 in two longitudinal rows, those of one row alternating with those 

 of the other. In most cases this arrangement is very clear but in 

 R. pingids the antheridia are sometimes in three or four irregular 

 rows, and in many species the arrangement of the archegonia 

 becomes indistinct by displacement. According to Miss Clapp 

 (6, p. i8i) the antheridia of A. pinguis arise in the usual way, one 

 for each segment, so that an arrangement here in three or four 

 rows must likewise be due to subsequent growth-displacements. 

 In a generalized type like A. pinguis the short male branches are 

 fleshy, and the structure is not very different from that of an 

 ordinary vegetative axis. Here, as elsewhere throughout the genus, 

 each antheridium is in a deep depression, connected with the out- 

 side by a circular opening. Otherwise no distinctive protective 

 structures are developed, although the thin margins of the branch 

 are more or less crispate without forming wings. In most species, 

 however, the male branches are more delicate in texture than the 

 rest of the plant, and distinct wings from one to several cells wide 

 are formed. These wings are sometimes spreading (see Figs. 9, 

 E, and 11, F) but are often suberect or even connivent (see Figs. 

 6, E, and 7, H), and thus represent a true protective structure. In 

 certain cases they are supplemented by bulging cells of the upper 

 surface of the branch, or even by appendicular outgrowths, in case 

 these are present elsewhere. Although in most cases the male 

 branches are quickly limited in growth this is by no means invaria- 

 bly the case. Sometimes twenty or more antheridia are formed, 



