556 ALEXANDER W. EVANS 



The sinuses are narrow and extend about half way to the center of the discs. 

 Except for the basal sinus, which is wider and deeper than the other the sinuses 

 are subequal in width and depth. As in other species of the genus various 

 irregularities are to be expected in the female receptacle, especially if the condi- 

 tions have been unfavorable for its full development. 



The thallus is variable in size but is usually '^ — cm. long and 5 — 12 mm. 

 wide. The upper surface is pale to dark green and rarely shows signs of 

 pigmentation. The lower surface, however, is pigmented with purple, sometimes 

 throughout its entire extent and sometimes in the median portion only. The 

 epidermal pores are of the cruciate type, the internal cells (normally four in 

 number) approaching each other closely and leaving a very narrow opening. 

 This type of pore is certainly implied by Goebel's account,^ where he states 

 that the opening can be reduced to a very narrow slit by means of the bounding 

 cells, even if it can not be closed completely. Stephani, however, states that 

 the opening is subquadrate, with oval bounding cells, showing that he may 

 have had a different species before him when he drew up his description. 

 The pores in M. foliacea are usually surrounded by six or seven rows of cells, 

 each row, except the innermost of the upper series, being composed of four 

 cells. The innermost row is usually composed of from six to twelve or four- 

 teen cells. 



The compact ventral tissue of the thallus, so far as observed by the writer, 

 is destitute of both slime cells and elongated sclerotic cells. GoEBEL states, 

 however, that cells of the latter type are present and figures them clearly in 

 both transverse and longitudinal view. In all probability the species is variable 

 and fails to develop sclerotic cells under very moist environmental conditions, 

 but the material available for study is too scanty to settle the question defi- 

 nitely. 



The appendages of the median ventral scales are ovate to suborbicular 

 in form and vary greatly in size, measuring 0.3 — o 9 mm, in length and 0.25 — 

 0.6 mm. in width. The apices may be blunt, apiculate, acute or short-acuminate 

 and the margins are either subentire or vaguely and irregularly sinuate-dentate; 

 it is only in the rarest instances that a tooth is apiculate at the apex. The 

 median cells of the appendages usually measure 50—60 [x in length and 35 — 

 45 [I. in width, while the marginal cells tend to be a little narrower. In most 

 cases there is no sharp distinction between the median and marginal cells, but 

 the latter sometimes extend at right angles to the margin and form an indistinct 

 border. 



Additional features of the female receptacle which deserve mention are 

 the stalk and the involucres. The stalk sometimes attains a height of 4 — 5 cm. 

 and shows a broad dorsal band of green tissue with air-chambers; on the oppo- 

 site side two furrows with rhizoids are {:)resent. The involucres are extremely 

 delicate and the material studied is insufficient to give a wholly satisfactor)' idea 

 of their features. It shows, however, that the free margins are rather densely 

 ciliate, and that there is some indication of lobes in addition, but these lobes 

 are apparently indifinite and separated by shallow sinuses. Mature spores are 

 about 21 [JL in diameter and show a yellowish or brownish color. xA distinct 



' Flora 96: 192, f. 143 (1906). 



