ARCHEGONIUM AND SPOROPHYTE OF TREUBIA INSIGNIS 269 
which is only slightly broader than the intermediate portion (seta), 
begins to show the first evidences of a differentiation of sporogenous 
tissue. 
In the development of the primary sporogenous tissue Treubia 
resembles most nearly, of the forms that have been investigated, 
Podomitrium. As in the latter the young sporogenous tissue is very 
vaguely defined, and it is quite impossible to determine exactly its 
extent (fig. 5, A). In this respect Treubia differs from Pallavicinia, 
Fig. 5. A. Upper part of young sporophyte, X 84; the sporogenous tissue is 
shaded. B. Two cross-sections of a sporophyte of about the same age as that 
shown in ^. C. Longitudinal section of an older sporophyte, X 27. 
Aneura or Fossombronia, where the limits of the young archesporium 
are much more definite, this being especially marked in Aneura and 
Fossombronia, where the archesporium is recognizable at a very early 
stage of development. 
The sporogenous region is bounded by several layers of sterile 
tissue, which form the wall of the capsule. This is about three cells 
thick at the sides, but at the apex of the capsule there may be as many 
as eight, and a conspicuous beak is produced as in Pallavicinia and 
Podomitrium, and to a lesser degree in Calycularia (fig. 6, A). In 
this respect Treubia also differs from Fossombronia and Aneura where 
the apical part of the capsule wall (aside from the elaterophore) is of 
the same thickness as the lateral wall. 
