1912] CLAPP—ANEURA PINGUIS 179 



On the ventral surface rhizoids (figs. 13-15) and mucilage hairs 

 (fig. 12) indicate slight cell differentiation. The rhizoids contain 

 chloroplasts at first like the other superficial cells (fig. 13). Such 

 cells project slightly, elongate, the chloroplasts disappear, and the 

 rhizoids look like root-hairs. As they grow longer the position of 

 the nucleus changes and the cytoplasm varies in amount and dis- 

 tribution. Both are near the somewhat thickened tip when the 

 rhizoid is old. The rhizoids resemble root-hairs in that they become 

 irregularly lobed in contact with soil particles (fig. 15) and flatten 

 out in a most deformed way against other thalli and bark. 

 Bolleter (2) notes this same lobing in Fegatella conica and it is 

 common among liverworts. The length and number of rhizoids 

 varies greatly. In contact with an underlying thallus or bark they 

 are very short (o . 09-0 . 16 mm.) ; in soil and moist air they average 

 less than 1 mm., and only occasionally reach 2 mm. On closely 

 appressed plants the rhizoids are numerous and scattered; in soil 

 they grow along the central axis but are never definitely localized. 

 Irregularity may come from fungi in the rhizoids, and again they 

 may be as straight as if uninfected. In no case were the lobes of 

 the rhizoids cut off by walls. 



Gemmae have been described by many for Aneura pinguis. In 

 the material at hand no gemmae were found. If they are charac- 

 teristic of this species, their absence must be due to the conditions 

 under which the plants grew. Evans (7) has found in species of 

 Metzgeria that gemmae are not likely to appear when the plant is 

 growing luxuriantly. This would account for their absence in the 

 field, but one might expect them to appear on plants grown under 

 less favorable conditions in the laboratory. 



Increase in the number of plants is brought about, as in many 

 other thallose liverworts, by the dying away of older parts, when 

 branches become the main axes of new individuals. 



Aneura pinguis produces three kinds of branches, the ordinary 

 vegetative ones and those bearing the two different sex organs. 

 Such branches have their origin in the segments of the apical cell. 

 All of the descriptions of this cell agree that it cuts off segments 

 on two sides alternately right and left (figs. 3-1 1). Vertical 

 sections through any of the marginal indentations which indicate 



