20 6 Lang . — On the Sporogonium of Notothylas. 
limits of foot, stalk, and capsule are thus clearly established at this stage, 
and continue to be traceable throughout the further development of the 
sporogonium. In the slightly older embryo seen in median section in 
Fig. ii the capsule has grown considerably. The whole course of the 
segmentation of the embryo thus agrees with the very uniform type for 
the Anthocerotaceae. In these young capsules the regions corresponding 
to the wall, the archesporium (derived from the amphithecium), and the 
columella in other Anthocerotaceae, can be recognized. All these regions 
are present in the zone just above the stalk, from which the intercalary 
growth proceeds. 
The difference between the mature capsule of this form of Notothylas 
and the typical capsule of the Anthocerotaceae depends on the different 
fate of the cells of the endothecium in the two cases. In Anthoceros this is 
devoted to the formation of the sterile columella. In this Notothylas it can 
only be called the columella on comparative grounds, for, as intercalary 
growth proceeds, the cells of the endothecium, as well as those of the 
amphithecial archesporium, give rise to sporogenous tissue. In this way 
the capsule, as has been shown above, comes to be filled with a uniform 
mass of spores and elaters. 
The differentiation of the tissues within the wall can be followed even 
in sections of advanced sporogonia, so that the absence of some of the 
intermediate stages from the material has been of little importance. Fig. 12 
is a detailed drawing of the median section of the sporogonium represented 
in Fig. 5, and includes the region from the stalk to the base of the capsule, 
where the distinction of elaters and spore-mother-cells is becoming esta- 
blished. In the stalk the endothecium appears as two rows of cells bounded 
by the amphithecium, consisting of a single layer. Just above this the 
amphithecium is seen to consist of two layers, the outer of which is con- 
tinuous when traced upwards with the wall of the capsule ; the inner can 
be followed upwards as a definite layer adjoining the endothecium, and is 
the archesporial layer. Though different in origin, the four rows of cells 
seen within the wall in Fig. 12 behave alike. Their cells undergo an 
ultimate transverse division, the upper segment forming one or more spore- 
mother-cells, while the lower gives rise to sterile elaters. In the figure the 
spore-mother-cells are shaded. Comparison with Fig. 6 will make it clear 
how the reticulum of sterile cells found in the mature capsule is derived. 
The relation of the uniform sporogenous tissue to the meristematic zone 
below in Fig. 12 demonstrates its origin from series of cells which corre- 
spond in other Anthocerotaceae, both to the archesporium and the columella. 
Further evidence of the complete absence of a sterile columella from such 
capsules is afforded by transverse sections of the basal region. In Fig. 13 
the limits of the four rows composing the endothecium and the surrounding 
groups of cells derived from the archesporium can be traced in the uniform 
