176 Alexander IV. Evans, 



The axis shows a Hving portion which is usually 2-3 cm. in 

 length, 0.8-1.5 mm. in width and 0.25-0.3 mm. in thickness (Fig. 

 10, D). The median portion is eight to ten cells thick, and the 

 decrease in thickness toward the rounded margins is gradual and 

 shght. Both surfaces are sHghtly convex (Fig. 10, E). On the 

 ventral surface a broad median band composed of narrow cells, 

 80-160 /along and only 20 /x wide, can be distinguished. These 

 cells are crowded with fungus hyphae and constitute the most 

 distinctive feature of the species. The remaining cells of the sur- 

 face layer are mostly 60-80 /x long and 30 fx wide, and their cavities 

 contain no hyphae; toward the sides of the thallus the surface- 

 cells decrease somewhat in length, the marginal cells being about 

 40 fi long. The interior cells are mostly 1 50-200 /* long and 30-50 

 jx wide, but an occasional cell indefinite in position and considerably 

 wider is sometimes present. Such a cell is shown at the left of the 

 figure and may be as much as 80 jx wide. Sometimes the cells next 

 to the fungus-bearing band of the ventral surface are narrow and 

 bear hyphae also, but the other interior cells usually lack them 

 completely. The cells throughout have slightly thickened walls. 



Branches arise at intervals of 1-3 mm. on each side of the axis 

 and spread obliquely. They are narrower than the axis, measur- 

 ing usually 0.35-0.7 mm. in width, but are essentially the same in 

 structure, the fungus-bearing band being distinct (Fig. 10, F). 

 An occasional branch represents a new axis and exhibits indefinite 

 growth, but most of the branches soon stop growing, although their 

 length may vary from 2 mm. to i cm. Sometimes even a primary 

 branch may be simple, but most of them bear from one to ten 

 secondary branches ; these in turn are usually simple but one or 

 two very short tertiary branches are sometimes produced. The 

 ultimate branches of whatever rank are mostly 2 mm. or less in 

 length, 0.2-0.45 mm. in width and about 0.15 mm. in thickness. 

 They show the same structure as the primary branches, the band 

 of cells with hyphae being still a striking peculiarity, but the median 

 portion is only six or seven cells thick. Branch-rudiments, which 

 rarely persist in the older parts of the thallus, are in the form 

 of very short bilobed projections, with the apical cell in the 

 indentation. 



A group of differentiated cells containing hyphae is a rare phe- 

 nomenon in the Jungermanniales and will at once distinguish 



