62 



MOSSES AND FERNS 



periclinal walls appear, but not at any stated time, so far as 

 could be made out, and the first ones do not, as Leitgeb asserts, 

 necessarily determine the separation of the archesporium, as in 

 the Corsiniese. The growth now becomes unequal, the cells in 

 the central zone not dividing so actively, a marked constriction 

 is formed, and the young sporogonium becomes dumb-bell 

 shaped. By this time a pretty definite layer of cells (Fig. 

 23, F) is evident upon the outside of the capsule, but the cells 

 of the globular lower part, or foot, are nearly or quite uniform. 

 They are larger than those of the capsule, and more transparent. 



Fig. 24. — Targionia bypophylla. A, Median longitudinal section of older embryo 

 enclosed in the calyptra (cflO> X80; B, a portion of the upper part of the same 

 embryo, X480; the nucleated cells represent the archesporium; C, part of the 

 archesporium of a still later stage; et^ elaters; sp, sporogenous cells, X480. 



In the latter the wall becomes later more definite, and remains 

 but one cell thick until maturity. The arrangement of the cells 

 of the archesporium is very irregular, and until the full number 

 of these is formed they are all much alike. Just before they 

 separate, however, careful observation shows that two well- 

 marked sorts of cells are present, but intermingled in a perfectly 

 irregular way A part of these cells are nearly isodiametric, 

 the others slightly elongated, and the nuclei of the former cells 



