290 Beer . — On the Development of the Spores of Riccia glauca. 
Fig. 6. Spore-mother-cell which is becoming rounded off. Secondary thickening layer forms 
strands between primary wall and tertiary thickening layer, x about 1100. 
Fig. 7. Spore-mother-cell. Synapsis (?). 
Fig. 8. Spirem-stage of the first division of the spore-mother-cell, x about 1100. 
Fig. 9. Chromosomes at equator of spindle. Secondary and tertiary thickening layers of the 
wall surround the spore-mother- cell. 
Fig. 10. Chromosomes at the equator of the spindle in first division of the spore-mother-cell. 
X about 1 100. 
Fig. 11. Anaphase of first division of the spore-mother-cell, x about 1100. 
Fig. 12. Chromosomes crowded together at the poles of the spindle, x about 1100. 
Fig. 13'. Telophase of first division of the spore-mother-cell, x about 1100. 
Fig. 14. Later stage of telophase. 
Fig. 15. Daughter-nuclei in resting condition before commencement of second division. Septum 
between cells not yet complete. 
Fig. 16. Daughter-nucleus from similar cell as in Fig. 14. Chromatin granules are aggre- 
gating together to form the compound nucleolus. 
Fig. 17. Second division of the spore-mother-cells. The septum between the cells now 
nearly or quite reaches the periphery, x about 1100. 
Fig. 18. Young tetrad with delicate septa between the cells and the periphery still clothed with 
secondary and tertiary thickening layers of mother-cell-wall. 
Fig. 19. Special-mother-cells. Examined in glycerine and congo-red. Thickening layers red ; 
middle lamellae and periphery colourless. 
Fig. 20. Spore with first spore- wall (drawn black) at the equatorial rim of the spore. 
Examined in glycerine and congo-red. Secondary thickening layers of special-mother-cell and 
mucilage at the rim of spores (both left white in the figure) stained red ; spore- wall yellowish. 
Equatorial mucilage limited internally by the plasma membrane alone, x about 1100. 
Fig. 21. Spore with first and second spore-walls in the neighbourhood of the equatorial rim. 
The second spore-wall still appears homogeneous. Examined in glycerine containing a very little 
fuchsin. 
Fig. 22. Spore at the equatorial rim. Early stage in the differentiation of the second spore-wall. 
Fig. 23. Older spore. Examined in calcium- chloride iodine. Second spore-wall differentiated 
into an outer distinctly laminated region and an inner apparently homogeneous region. In the 
present case the darkly coloured layer is only just appearing between the two regions at this 
comparatively late stage. 
Fig. 24. Portion of spore-wall after warming in a mixture of chromic and sulphuric acids, washing 
and examining in calcium-chloride-iodine solution. Laminated structure of first spore- wall and outer 
region of second spore-wall is well shown. Intimate union exists between remains of thickening 
layers of special-mother-cell walls and first spore-wall. Both first and second spore-walls colour 
yellow, x about 1100. 
Fig. 25. Somewhat older spore treated similarly to the one drawn in Fig. 24. All the mem- 
branes colour yellow. x about 1 1 00. 
Fig. 26. Older spore from microtome section stained with Pleidenhain’s haematoxylin and 
bismarck-brown. Dark-coloured layer between inner and outer regions of the second spore-wall is 
very conspicuous. A similar, but narrow, dark layer lies between the second spore-wall and the 
endospore. x about 1100. 
Fig. 27. Nuclei from developing spores : 
(а) from spore with first spore- wall only ; 
(б) from spore with two spore- walls but second wall still homogeneous; 
(c) from older spore with thick, differentiated second spore- wall. 
PLATE XXII. 
B. PHOTOGRAPHS . 
Fig. 28. Archegonium showing fertilization of the egg-cell. 
Fig. 29. Sporangium containing spore-mother- cells ; calyptra two-layered. 
Fig. 30. Spore-mother-cells becoming rounded off and separated from one another. 
