Beer . — On the Development of the Spores of Riccia glaucct. 289 
spore, gives the reactions of pectose and cellulose. It is often separated 
from the second spore-wall by a very thin band of dark-coloured material 
similar to that which occurs in the gap between the two regions of the 
second spore-wall. 
19. No silica could be detected in the spore-membranes. 
20. The protoplast of the spore is actively concerned in the growth of 
the membranes which surround it. The intimate union which exists 
between each new lamella, which is being added to the wall, and the 
protoplast in itself indicates this fact, whilst the curious spirem-like 
structure of the spore-nucleus, resembling that of certain animal cells, also 
suggests the occurrence of active metabolic processes in the cell; 
a 1. The actual material necessary for the growth of the spore-walls is 
partly derived from the breaking down of the parietal cells of the sporangium 
and of the inner layer of the calyptra. This source is most probably 
supplemented by material which is assimilated by the vegetative cells of 
the thallus, and -which diffuses into the sporophyte in a state of solution. 
22. After the first spore-wall has been formed, and during all the 
earlier periods of the growth of the second spore-wall, a quantity of 
mucilage is constantly present in the sporangium between the spore- 
tetrads. The origin and significance of this mucilage are, however, still 
somewhat obscure. The various possibilities of the case are discussed in 
the body of the paper. 
In conclusion I should like to express my thanks to Professor J. B. 
Farmer, F.R.S., for kindly examining my sections and for offering several 
valuable suggestions. 
EXPLANATION OF FIGURES IN PLATES XXI AND XXII. 
Illustrating Mr. Beer’s paper on the Spores of Riccia. 
All Figures refer to Riccia glauca. 
PLATE XXI. 
A. DRAWINGS. 
Fig. 1. Spore-mother-cell. Resting nucleus showing lobular nucleolus. 
Fig. 2. Spore-mother-cell. Nucleolus of resting nucleus broken up into distinct granules. 
Fig* 3 . Nucleoli of nuclei from the apex of the thallus showing chromatic granules embedded in 
a matrix. 
Fig. 4. Sterile parietal cells of sporangium in which the mother- cells were becoming rounded off. 
Fig. 5. Spore-mother-cells which are separating from one another. Where they are still attached 
a middle lamella (the primary wall) and secondary and tertiary thickening layers can be recognized, 
x about 1 100. 
