284 Beer . — On the Development of the Spores of Riccia glauca. 
times it is discernible at a very early stage in the history of the second 
spore-wall. Sometimes the spore has become much older and the second 
spore-wall has become quite a thick structure before any signs of this layer 
can be seen \ Again its appearance is sometimes nearer, sometimes further 
away from the outer periphery of the spore-wall. In preparations which 
have been treated with a mixture of chromic and sulphuric acids a separa- 
tion of two sets of lamellae can often be seen in the second spore-wall with 
an evident gap between them. Further evidence is given by a study of 
older spores in which a similar but much narrower black band can usually 
be seen between the inner boundary of the second spore-wall and the 
endospore (Fig. 26). What the nature and origin of the substance which 
occupies this space may be is quite unknown. It does not seem unlikely, 
however, although I can bring forward no proof for the view, that the dark 
substance which collects in the gap of the spore-wall is the material which 
colours brown the older spore-walls throughout their thickness. 
Most instructive preparations of the spore-wall at the middle periods 
of development may be obtained by treating sections with a mixture of 
chromic and sulphuric acids, washing and then examining them in chlor- 
zinc-iodine or calcium-chloride-iodine. The first spore-wall is coloured 
yellow and shows a densely laminated structure. Within this wall lies the 
second spore-wall. The outer portion of this wall is seen to be composed 
of loosely arranged lamellae which sometimes lie closely against the first 
spore-wall but which have usually become separated from it by the action 
of the reagent (Figs. 24, 25). The inner portion of the wall, which is 
generally separated from the loose lamellae by a gap, has a homogeneous 
appearance and no lamellae can be distinguished in it. If the action of 
the acids has been carried to the right point it can be seen that the inner 
part of this internal layer of the second spore-wall gives beautiful cellulose 
reactions with the iodine reagents. The band of cellulose is considerably 
thicker on the dorsal surface of the spore, whilst cuticularization had 
become more complete over the ventral surfaces. Congo-red in dilute 
solution also colours the cellulose areas a deep red. 
Although the inner portion of the second spore-wall has a homo- 
geneous appearance, even after the action of reagents, it is nevertheless 
really built up of successive lamellae. 
During the development of the spore this inner region of the second 
spore-wall grows very considerably in thickness, and the sections show 
with unmistakable clearness that this growth is due to the deposition of a 
series of lamellae upon one another. The newest lamella is formed by the 
protoplast of the spore in the most intimate attachment with the plasmatic 
membrane. By plasmolysing the protoplast this lamella is usually at the 
same time separated from the walls of the spore and the contracted proto- 
1 The late appearance of this dark layer is shown in Fig. 23. 
