632 Price . — Dark-ground Illumination . 
Wisselingh, C. van : Tests for Tannin in Spirogyra. Proc. Konink. Akacl. van Wetenschappen, 
vol. xii, 2nd part, July, 1910, pp. 684-705. 
Zeiss, Carl : Pamphlets on Dark -ground Illumination. 
Zsigmondy: Colloids and the Ultramicroscope. Eng. trans. Wiley and Sons, New York, 1909. 
EXPLANATION OF PLATES XLI AND XLII. 
Illustrating Mr. S. R. Price’s paper on Dark-ground Illumination. 
PLATE XLI. 
Fig. 1. Spores of Mucor in various stages. ( a ) Fresh spores showing slightly granular 
structure. ( b ) Spores after swelling in water for a few hours, with colloid hydrosol contents. 
(<r) Early stage of germination. ( d ) Later stage, showing the fine colloid particles in the spore 
cavity and the protoplasmic plugs in the hypha. 
Fig. 2. Cell of Spirogyra plasmolysed with dilute glycerine, showing fine fibrils. Note the 
structure at the base ( a ) and the minute attaching disc (b) as well as the larger microsomes. 
Fig. 3. Portion of plasmolysed cell viewed in three depths of focus, (a) The outer wall of the 
vesicle, showing fine particles which exhibit an oscillating movement. ( b ) The interior of the 
vesicle with enclosed sap particles, also the general structure of the protoplast. (0) Outer focus, 
showing extremely fine particles (for description see text). 
Fig. 4. Cell of Spirogyra , showing a vesicular plasmolysis treated with dilute potash. The 
thin walls of the vesicles (cf. Fig. 3) become coarse structured and opaque, while the whole proto- 
plast, except the chloroplast, becomes somewhat milky. 
Fig. 5. Portions of two cells of Spirogyra fixed with osmic acid, (a) Outer focus ; the micro- 
somes are still evident and the gel is fairly clear. ( b ) Inner focus, showing the fine precipitate 
produced by the tannins. 
Fig. 6. Single cell from leaf-edge of Elodea canadensis , showing chloroplasts ( c ), proto- 
plasmic microns ( p ), and sap particles (s). 
Fig. 7. Cell from leaf-edge of Elodea canadensis plasmolysed with 10 per cent, potassium 
nitrate. Note the fine protoplasmic threads connecting the balled-up portions of the protoplast to 
one another and to the walls; also the crystalline sap particles inside the vacuoles. 
Fig. 8. Living nucleus of cell of Elodea canadensis with appearance of translucent ‘ hydrogel ’ 
microsomes of protoplasmic stream passing over nucleus. 
Fig. 9. Nucleus of same, fixed with glacial acetic acid, showing coarse hydrogel structure 
producing overlapping diffraction images. 
PLATE XLII. 
Fig. 1. Nucleus of Spirogyra with surrounding cytoplasm and suspending threads. The almost 
clear hydrogel of the nucleus, and the nucleolus, are shown. The microsomes of the cytoplasm are 
very distinct. 
Fig. 2. Suspending threads and cytoplasm surrounding the nucleus in a species of Spirogyra. 
Nucleolus not distinguished. 
Fig. 3. Portion of hair of Cucurbita plasmolysed with 30 per cent, cane sugar. Three vesicles 
produced enclosing some sap particles ; vesicle walls of thin membrane with scattered very fine 
particles. 
Fig. 4. Portion of hair of Cucurbita plasmolysed with 30 per cent, cane sugar. Note the 
structure of the protoplast with external layer and fine particles below it, coarser particles in the 
interior. 
Fig. 5. End of cell of Spirogyra plasmolysed in 10 per cent, potassium nitrate solution, showing 
coarser threads than in PI. XLI, Fig. 2. 
Fig. 6. Diagrammatic drawings of sap particles from Elodea in different positions, (a) Crystal- 
line. (< h ) Vesicular. 
