270 Alexander W. Evans, 



slightly thickened walls, sometimes in two layers, mostly 30-60/A 

 long (averaging about 45iu.) and 15-30/1. wide (averaging about 

 23/i), papillae absent; pores (with their surrounding cells) 

 mostly 90-I30/A long and 70-80/* wide, surrounded usually by six 

 (or seven) rows of cells (three or four in the upper and three 

 in the lower series), the two lower rows of the upper series 

 usually composed of eight (six to ten) cells apiece (more rarely 

 of only three to five cells), the other rows of four (three to 

 five) cells apiece, inner opening usually four-sided, more rarely 

 three- or five-sided, with the sides straight or nearly so, the 

 bounding cells more or less obscured by a resinous deposit ; air- 

 chambers of medium height, isodiametric or somewhat elongated, 

 their boundaries sometimes distinct and sometimes vague when 

 viewed through the epidermis, present everywhere, rows of 

 photosynthetic cells often four or five cells long but sometimes 

 shorter; compact ventral tissue about twenty cells thick in the 

 median portion, the walls sometimes pigmented, more or less 

 thickened and showing distinct pits, sclerotic cells usually dis- 

 tinct, scattered, mostly five to thirty in a cross-section, more 

 abundant in the median portion but sometimes present in the 

 wings, in the latter case often distinctly visible without section- 

 ing, slime-cells lacking; ventral scales in two distinct rows, the 

 laminar scales alternating with the median scales and not much 

 nearer the margin ; appendages of the median scales broadly 

 lanceolate to ovate, when well developed mostly 0.35-0.6 mm. 

 long and 0.27-0.45 mm. wide but sometimes considerably smaller, 

 apex apiculate, acute, or cuspidate, margin more or less densely 

 denticulate or dentate, the teeth usually one or two cells long, 

 cells showing a gradual and slight decrease in size toward the 

 margin, median cells usually longer than broad, mostly 40-80/x 

 long and 20-40/1 wide, marginal cells mostly 20-40/x long and 

 15-20/* wide, irregular but the long axis usually at right angles 

 or nearly so to the margin, cells containing oil-bodies apparently 

 always lacking: male receptacle borne on a stalk 5 mm. long 

 or less, with two to four rhizoid-f urrows and a single broad dorsal 

 band of air-chambers, the disc variable in size but mostly 6-8 mm. 

 broad, deeply lobed, the lobes or rays usually four to six but 

 sometimes two, three, seven or eight, palmately disposed, the 

 basal sinus a very broad angle or a straight line, mostly 3-6 mm. 

 long and 2-3 mm. wide, rounded, with a thin wavy margin extend- 

 ing across the basal sinus, ventral scales imbricated, in two or 

 more rows; female receptacle borne on a stalk 1.5-2 cm. high, 

 with two to four rhizoid-furrows and a single broad dorsal 

 band of air-chambers, the disc mostly 5-7 mm. wide, the lobes 

 or rays spreading at maturity, extending about half way from 

 the margin to the center, normally seven but often only five or six, 

 more rarely eight to eleven, slightly or not at all dilated at the 

 truncate, irregularly crenate or slightly emarginate apex, upper 



