138 BOTANICAL GAZETTE [august 



duration. The gametophyte body retains this massive form 

 until after the resting period. 



The second period of growth begins by the formation of a cuneate 

 apical cell. A terminal cell is cleft by a wall inclined about 30 

 with reference to the longitudinal axis of the spore; a second 

 inclined wall bisects the first at an angle of approximately oo°; 

 lateral walls complete the cuneate apical cell (tig. 41). The latter 

 cuts off dorsal and ventral segments (fig. 42) as well as lateral 

 segments (fig. 43). Such a method of growth is characteristii of 

 the young gametophyte until about the time of antheridium 

 formation. 



The growth of the third period is by means of a lenticular 

 cylindric apical cell (fig. 47). The transition is somewhat irregular. 

 Sometimes the apical cell is more or less equally divided; then the 

 two halves simultaneously cut off cells (fig. 45) which correspond 

 to the dorsal and ventral segments of the preceding form. The thal- 

 lus in cross-section has the appearance of being medianally divided 

 by a wall. Another transition form is shown in fig. 44. As the 

 thallus becomes thicker the posterior angle becomes greater, the 

 two faces being finally replaced by one which is curved. The cells 

 cut oft" from the posterior face divide rapidly; as many as 6 segments 

 may be formed before the next division occurs. The rapid division 

 of the laterally placed cells causes the wings to be protruded out- 

 ward and forward (figs. 46, 48, 49). There has been much dis- 

 cussion regarding the method of branching. Hofmeister 3 believed 

 that the central papilla ("Mittellappen") shown in fig. 14 was the 

 seat of the chief apex; hence that there is no true dichotomy. 

 Leitgeb 4 states that the origin of the central papilla is from a 

 marginal cell. When branching takes place, the apical cell, 

 instead of cutting off a lateral segment, divides equally or almost 

 so; each of these daughter cells assumes apical characters. The 

 central papilla is produced by the crowding together of lateral 

 segments from the two apical cells. It later develops into a 

 central lobe corresponding to fused wings. Branching is essentially 



> Hofmeister, W., Higher Cryptogamia. Ray Society. 1862. 

 4 Leitgeb, H., Untersuchungen iiber die Lebermoose. 1882. Vols. II and III. 

 Jungermannieen. 



