178 MOSSES AND FERNS chap. 



ment, and his account agrees in the main with Leitgeb's/ 

 except as to the relation of the columella and outer spore-sac. 

 The first divisions in the embryo correspond exactly to those 

 in AndrecBa and the Bryineae, and for a time the young embryo 

 grows from a two-sided apical cell. The secondary divisions 

 in the segments, however, are quite different from that observed 

 in any other Moss, and are like those in the antheridium. 

 Instead of the first wall dividing the segment into equal parts, 

 it divides very unequally. The second wall strikes this so as 

 to enclose a central cell, triangular in cross-section, which with 

 the corresponding cell of the adjacent segment forms a square. 

 This square, the endothecium, does not therefore at first show 

 the characteristic four-celled stage found in all other Mosses. 

 The amphithecium becomes ultimately three-layered, and be- 

 tween the second and third layers an intercellular space is 

 formed, as in the Bryineae, but this extends completely over the 

 top of the columella. The most remarkable feature, however, 

 is that no archesporium is differentiated, but any cell of the 

 endothecium may apparently become a spore mother cell. The 

 number of the latter is very small, seldom exceeding five or six. 

 They become rounded off, and gradually displace the other 

 endothecial cells, which doubtless serve as a sort of tapetum for 

 the nourishment of the growing spores. Each spore mother 

 cell as usual gives rise to four spores, which are here very much 

 larger than in any other Moss. A section of the ripe sporo- 

 gonium (Fig. 8i) shows that only one of the primary three 

 layers of amphithecial cells can be recognised except at the 

 extreme apex and base. The seta is present, and a foot, much 

 like that of Andrecsa, and penetrating into the tissue of the 

 stem apex, is seen. 



Leitgeb is inclined to look upon Archidimn as a primitive 

 form allied on the one hand to AndrecEa and on the other to 

 the Hepaticae, possibly Notothylas. However, as his assumption 

 that the latter has no primary columella has been shown to be 

 erroneous, his comparison of the whole endothecium o{ Archidimn 

 with that of Notothylas cannot be maintained, as we have shown 

 that in the latter, as in Ant]wceros^ih.& archesporium arises from 

 the amphithecium, and not from the endothecium, as is the case 

 in Archidimn. Inasmuch as the gametophyte and sexual 

 organs of Archidimn are those of the typical Mosses, it seems 



^ Leitgeb (8). 



