The Genus Riccardia in Chile. 121 



cells. The median portions of the ultimate branches are six or 

 seven cells thick. The central part is occupied by two or three 

 layers of thick-walled cells, forming a narrow strand and covered 

 over, both above and below, by layers of cells similar to the wing- 

 cells. In the primary branches the structure is much the same as 

 that just described, but the central strand of the median portion is 

 thicker and the wings ma}^ be four cells thick in places. 



In rare instances a branch is formed which represents a new 

 axis. It takes its origin between two photosynthetic systems, 

 diverging but slightly in direction from the main axis, and 

 eventually gives rise to a separate individual. Another type of 

 branch which is more frequent and yet only sparingly produced is 

 the stolon. A branch of this character occupies the same position 

 as a new axis and is sometimes so close to the lower of two pho- 

 tosynthetic systems that it seems to be axillary in origin. A stolon 

 soon grows downward and may attain a length of 5 mm. or more, 

 a width of 0.35 mm. and a thickness of 0.25 mm. It is sparingly 

 and irregularly branched and shows a structure similar to that of 

 the main axis, except that the zone of thick-walled pigmented cells 

 is thinner and less well defined. 



The inflorescence of R. prchcnsilis is dioicous. The male 

 branches usually arise as the secondary branches of a primary 

 photosynthetic axis. In typical cases an axis of this character 

 first bears a few vegetative branches, then from three to six pairs 

 of male branches, and then a few more vegetative branches before 

 the growth of the system is brought to an end. This typical con- 

 dition, however, is not always realized, and a male branch may even 

 be borne on a secondary photosynthetic axis, thus representing a 

 tertiary branch. The male branches are simple and are almost 

 wholly occupied by the terminal inflorescences, sterile proliferations 

 being exceedingly rare. Instead of spreading widely the male 

 branches scarcely spread at all, being often partially concealed 

 beneath the wings of the primary branch. The inflorescences are 

 laterally compressed and are usually 0.9-1.4 mm. long and 0.3-0.45 

 mm. wide. The marginal wings, which are erect or connivent, are 

 two or three cells wide and distinctly crenulate or denticulate from 

 projecting cells. The antheridia are mostly eight to sixteen, in 

 two longitudinal rows, and the openings of the antheridial chambers 

 are usually separated from one another by two rows of slightly 



