METHODS 21 



The young antheridium arises very near the apex of the thallus, as a 

 single large cell, projecting from the side of the midrib (Fig. 10, A). 

 The first division wall is transverse, and separates a basal cell which 

 takes no part in the development of the antheridium itself, and an outer 

 cell, which is the real mother-cell of the antheridium (Fig. 10, B). At 

 about the same time that this transverse division is formed in the young 

 antheridium, certain neighboring superficial cells of the midrib become 

 evident, which later form special structures accompanying the antheridia. 

 Some of these "companion cells" secrete the mucilage which bathes the 

 young antheridia; while others, not always readily distinguishable from 

 the earliest stages of the antheridia themselves, finally develop into the 

 characteristic scales covering the older antheridia, somewhat as described 

 by Campbell [i] for Aneura. 



The divisions in the antheridium show some variation. Of the two 

 cells formed by the first transverse wall, the inner one divides by a verti- 

 cal wall into two cells, which remain sunk in the midrib and usually divide 

 no further (Fig. 10, C-E), and may usually be recognized at the base of 

 the stalk in the fully developed antheridium. 



The first wall in the antheridium itself is also transverse. Of the 

 two cells thus formed, the lower gives rise to the stalk of the antheridium, 

 and also to the layer of cells separating the sperm-cells from the stalk of the 

 antheridium. The outermost of the two original cells divides first by a 

 median vertical wall, and each of these cells is next divided by a nearly peri- 

 clinal wall into two very unequal cells. This wall intersects both the out- 

 side wall of the antheridium and the median wall, and is quickly followed 

 by a second similar wall which meets the first one and also intersects the 

 median wall. A cross-section of the antheridium at this stage (Fig. n, 

 A) shows two triangular central cells surrounded by four narrow per- 

 ipheral ones. The young antheridium at this stage closely resembles 

 that of Porella Bolanderi (Campbell [i], Fig. 52), and differs from the 

 usual type of the Jungermanniales, where, according to Leitgeb ([1], II, 

 p. 44) these two peripheral cells do not extend to the top of the anther- 

 idium, and a third peripheral cell is cut off before the separation of the 

 central cell is complete. The appearance of longitudinal sections of the 

 young antheridium, cut respectively in the plane of the first median wall, 

 and at right angles to it, are shown in Fig. 10, D, G, E, H. Cross-sections 

 of similar stages are shown in Fig. 11, A, C. The next divisions take 

 place in the peripheral cells, and in the stalk, the two primary spermato- 

 genous cells remaining undivided until the stalk is well developed and 



