56o 



ALEXANDER W. EVANS 



width and 0.12 mm. in thickness. Tertiary branches arise only when the sec- 

 ondary branches are more vigorous. In their histological features the branches 

 are essentially like the main axis, but the [)rimary branches (Fig. i, E) are 

 only about six cells thick in the middle and the secondary branches only four 

 or five cells. In most cases the marginal wings with their crenulations are more 

 distinct on the branches (Fig. i, G, K) than on the main axis, and the ventral 

 slime papillae show a definite arrangement in two longitudinal rows. The 

 branches show clearly also the gradual decrease in the size of the surface-cells 

 in passing from the median portion to the margin. 



Although marginal wings and crenulations are distinctive of the species, 

 they are not necessarily present on every vegetative axis. Sometimes the main 

 axis (Fig. i, H) or even a primary branch (Fig. i, F) is rounded or bluntly 

 pointed in cross section. Under such circumstances the surface-view does not 

 show a wing or even a clearly differentiated row of marginal cells, and the 

 thallus is bounded by a continuous line. 



Attention may be called also to two modifications which the secondary 

 branches or the apices of the primary branches sometimes undergo. In one 

 of these modifications the branches are only 0.15-0.2 mm. in width and are 

 flatter than ordinary branches. They present, in fact, a strongly metzgerioid 

 appearance, the narrow costa being sharply marked off from the unistratose 

 wings (Fig. i, I). The other modification is equally narrow but is only slightly 

 flattened and shows no differentiation into costa and wings (Fig. i,J). Branches 

 of this t\pe ma)' be interpreted as stolons; they seem to arise without any 

 regularity (Fig. i, B), although in some cases they may be present on one side 

 of an axis but not on the other (Fig. i, C). 



The inflorescence of R. brcvirainosa seems to be invariably dioicous, as 

 stated by Stephani. The male branches usually arise, either singly or in sub- 

 opposite pairs, from the base of a primary branch, but in some cases they are 

 borne directly on the main axis. The inflorescence, which is often more or 

 less recurved, occupies the greater part of the branch and usually measures 

 0.4 — 0.6 mm. in length and 0.3 mm. in width. The antheridia in most cases 

 number from four to sixteen, and the openings into the antheridial chambers 

 are usually separated by two rows of cells. The wings are only one cell wide 

 but are distinctly crenulate. As a rule they are erect or somewhat connivent, 

 thus partially concealing the upper surface of the inflorescence. 



The female branches agree with the male branches in their position, being 

 borne either on the main axis or at the base of a primary branch. The arche- 

 gonia are usually abundant and may number sixteen or even more. The wings 

 are divided up into irregular lobes, blunt or sharp at the apices and usually 

 five to seven cells long. They are supplemented by similar outgrowths in 

 connection with the archegonia. In rare cases a female branch may continue 

 its growth beyond the inflorescence and form a simple or branched expansion 

 of the usual vegetative type. The »calyptra» is about 0.6 mm. in diameter and 

 may attain a length of about 2 mm. The corona is not distinct, but the entire 

 surface of the calyptra is covered o\'er with crowded and irregular projecting 

 cells or groups of cells. 



