20 7 
Lang . — 6b* Sporogonmm of Notothylas. 
sporogenous tissue. These limits continue to be traceable, even in the 
zone at which the spore-mother-cells are differentiated, and Fig. 14 a and b , 
which are two successive sections of the sporogenous tissue at this level, 
afford additional proof of the sporogenous nature of the endothecium. 
For the greater part of the intercalary growth in all the sporogonia 
examined the endothecium and archesporium behave alike as described 
above. In many sporogonia a sterile columella appears towards the close 
of growth. This results from the intercalary meristem of the endothecium 
becoming in whole or part sterile. The change is apparent as soon as the 
sporogenous cells acquire the dense appearance by which they contrast 
with the cells of the wall of the capsule. When one or more quadrants 
of the endothecium have become sterile, they also stand out in contrast to 
the sporogenous cells (Fig. 1 5 d, e ; Fig. 16). The series of transverse 
sections in Fig. 15 illustrates a case in which one quadrant of the endo- 
thecium had become sterile, while the other three were sporogenous. This 
series extends from the stalk to the region where the elaters and mother-cells 
are distinguishable, and may be compared with the longitudinal section in 
F'ig. 12. In the longitudinal section through the base of another capsule 
(Fig. 16) a short columella, derived from the whole thickness of the endo- 
thecium, is shown. Such short columellas were found at the base of some 
fully mature capsules, and did not appear to undergo any disintegration into 
separate cells. In the numerous capsules examined the sterilization only 
supervened shortly before the completion of intercalary growth. The arrest 
in growth was in no way dependent on decay of the stalk, and Leitgeb’s 
suggestion to this effect seems to be without proper foundation. It seemed, 
on the other hand, to be associated with the maturing of the spores at 
the tip of the capsule. When these have acquired their dark-coloured 
walls, a change which extends downwards towards the base of the capsule, 
active growth appears to cease. 
We may sum up the chief features of the development and structure 
of the sporogonium in this form, by saying that the embryogeny conforms 
to the usual type for the Anthocerotaceae , but that the endothecium , instead 
of being devoted to the formation of a sterile columella , for 7ns sporogenous 
tissue for the greater part of the intercalary growth of the sporogonium. 
In a considerable proportion of cases , hoivever , it produces sterile tissue 
tozvards the close of development. 
Other investigators have shown that in N. Breutelii there is sometimes 
a complete sterile columella, and this doubtless arises by the endothecium 
being sterile from the first. The range of variation in the development of 
the internal tissues of the embryo may fairly be assumed to be dependent 
on physiological factors which vary from individual to individual, and not 
in this case to be of value as an indication of specific difference. That the 
majority of the sporogonia in a single small collecting should show the same 
