24 MINNESOTA BOTANICAL STUDIES. 



The holdfast is a disc about i cm. across, and may be some- 

 what lobed at its margin, due to protruding masses of cells that 

 are somewhat rhizoid in function, tending to clasp the irregu- 

 larities of the substratum. The under surface appears slightly 

 rough and pitted. 



The mature stipe is elliptical in cross-section, but not winged. 

 It is thicker and rounder at the holdfast, but flattens out into a 

 ribbon-like shape farther up, and widens and thickens slightly 

 toward the top. The average width at the bottom is 3 mm., 

 and at the top 4 mm. It is about 1 mm. thick at the base and 

 2 to 3 mm. at the top. It is tough and coriaceous below, soft 

 and fleshy above. 



The laminal portion is usually two-lobed, and is differentiated 

 externally from the stipe by a rather abrupt thickening and by 

 the fact that it is generally dotted over with the elevated ostioles 

 of the conceptacles, giving it a warty appearance. The lamina 

 is also more translucent than the stipe. The lamina is wedge- 

 shaped ; the lobes into which it is divided in its upper half are 

 tapering with rounded points. The laminae have the softest 

 tissue in the plant. There are usually laminse in all stages of 

 development, on a main branch, from cylindrical stipe-like 

 laminae to old, flat, warty, fruiting ones. 



The color of the plant is nearly uniformly light brown, the 

 older parts being a little darker, especially the lower stipe. 

 The surface, except on the fruiting lobes, is smooth and shining. 

 The plant is very elastic. 



Adventitious shoots may arise on any part of the surface of 

 the plant. They occur chiefly where old wounds have healed 

 over. For instance, where a branch has been torn of, or a 

 lamina cut off, or where incisions have occurred, here may be 

 found proliferations arising as small outgrowths. Sometimes 

 only one may occur, again a dense cluster. Some of these de- 

 velop into large shoots. 



The conceptacles may easily be seen by looking through the 

 translucent lamina toward a strong light. They are thickly 

 scattered over the lamina and its lobes. There is a rude ar- 

 rangement of the conceptacles in rows running approximately 

 perpendicularly across the axes of the lobes. There are 150 to 

 200 conceptacles on a lamina. They are developed in the 

 younger tissue at the ends of the lamina lobes. Hence the 

 more mature conceptacles are found some distance from the tip 



