COMPARISON OF SPOROGONIA 285 
cells of the columella! Such facts again indicate a probability that 
the whole product of the endothecium was fertile in more primitive 
forms. 
A general comparison of the sporogonia of Mosses (excluding the 
Sphagnaceae) thus leads to the conclusion that two distinct tissue-tracts 
are consistently produced in them by early segmentation, the endothecium 
and the amphithecium. As these are differentiated early, and with great 
constancy, while they differ also in their products, they are to be accepted 
as morphologically distinct. The amphithecium is always sterile, and to its 
modifications the chief mechanical and assimilatory tissues owe their 
origin; the modifications may involve expansion of tissues, but no initia- 
tion of new parts. The endothecium, theoretically fertile in the first 
instance throughout its length and breadth, underwent progressive sterili- 
sation, parts of it being diverted to other uses: a central tract became 
the sterile columella, while the fertile region became abbreviated both 
at its upper and lower limits; and thus the actual archesporium in 
typical Bryales is a mere truncated residuum, with its barrel-like form 
open at both ends: the structural indication that its origin was as thus 
suggested is seen in its apparently arbitrary limitations at either end 
{compare Figs. 135, 136, 139). 
This is well illustrated in Fusaria and Phascum, where there is a 
continued growth with an initial cell at the apex. of the sporogonium ; 
the archesporium appears in longitudinal sections of young sporogonia as 
a definite row of cells on either side of the columella; but it is impossible 
at first to tell in those rows of cells where the exact limit of spore- 
development will be. Below the lower limit the cells of the row develop 
sterile, above it fertile; but in either case the segmentations which define 
the cell-row are the same. Passing to the apex, the archesporial row is 
continued beyond the limit of fertility: passing downwards, the cell 
row may also be traced into the seta: structurally the possibility of 
further spore-production seems to be there, but arrested. In different 
types of Mosses the fertile zone thus limited is not always located at 
the same level in the sporogonium as a whole: it is sometimes preceded 
by a shorter, sometimes by a longer, seta. By comparison of these 
different types, an idea is acquired of a residual and limited fertile zone, which 
has been liable to be shifted in the course of descent; and such shifting 
is made possible by the continued apical growth seen in the developing 
sporogonium. It is important to have a clear conception of the fertile 
zone as a residuum thus movable in the course of descent; the vari- 
able balance thus established between sterile and fertile tissues is not 
only interesting in its bearing on the study of sporogonia, but it will 
come into comparison later with similar features seen in certain strobiloid 
1Lantzius Beninga, Bedtr. z. Kenntn. d. Mooskapsels, 1847, Tab. 58, Figs. 9’, 9”. 
Also Kienitz-Gerloff, Bot. Zect., 1878, p. 47, Taf. 2, Fig. 52. 
