270 BRYOPHYTA 



to have the intercalary activity unlimited. Moreover, in these small 

 sporogonia, though a sterile columella is often present, sometimes its 

 place is taken by/ fertile tissue ; and the difference may be seen in sporo- 

 gonia of the same species. The details of this were long ago described 

 by Leitgeb/ but doubts have since been raised regarding his conclusions by 

 investigators who, working chiefly with other species, did not obtain the 

 same results. 2 Recently, however, Lang has made observations which go 

 far to explain the discrepancies ; and though they do not exactly coincide 

 with Leitgeb's account as regards the development of Notothylas, they show 

 that, as regards the fertility of the columella, he was substantially correct. 3 

 It appears that the embryonic structure of the sporogonium of 

 Notothylas is essentially like that of Anthoceros, in respect of the relations 

 at its base of columella, archesporium, and capsule-wall. In those cases 

 where the columella is present in the mature state, the spore-mother-cells 

 originate only from the archesporium. But in other cases where a definite 

 columella is not present in the mature state, any cell of the tract laid 

 down structurally as columella may become a spore-mother-cell. Many 

 do so, and thus, as Leitgeb described, the place of the sterile columella 

 may be taken by a spongy mass of sterile tissue, in the meshes of which 

 the spores are included. In addition to this, however, fertile cells and 

 elaters are also produced from the archesporium, which lies, as in 

 Anthoceros, outside the columella (Figs. 131 A-F). Two interpretations 

 of this state are possible : either that the columella-less forms are primitive, 

 and their partly fertile condition intermediate towards the establishment 

 of a completely sterile columella : or that the forms with a columella are 

 primitive, and the columella-less forms a reversion, some of its cells 

 resuming fertility which had previously been lost. Dr. Lang is inclined 

 to consider the columella-less forms as reduced : but whether reduced or 

 not the facts throw considerable light upon the relation of the columella- 

 less to the columelloid forms: they increase the justification for considering 

 the central group of cells, which in all other Anthocerotaceae is wholly 

 devoted to the formation of a sterile columella, as the original sporogenous 

 tissue, and the amphithecial archesporium as of secondary origin. The 

 duty of producing spores would seem to have been transferred from the 

 central to the superficial set of cells. It is thus possible to bring the 

 apparently divergent sporogonium of the Anthocerotales into relation to 

 that of the simpler and probably more primitive Jungermanniales. The 

 causes of the change of the products of the endothecium from the fertile 

 to the sterile condition must be looked for in influences acting on the 

 primary meristematic tissue of the embryo, or on the intercalary zone of 

 secondary meristem. Dr. Lang holds 4 that the idea of grouping of elaters 

 in a central position to form the columella is not in this case in accordance 



1 Lebermoose, v. , p. 39. 



Mottier, Bot. Gas., 1894; Campbell, Mosses and Ferns, Edn. ii., pp. 151-155. 

 3 Lang, Ann. of Bot., vol. xxi., p. 201, etc. 4 Z.r., p. 208. 



