Life- History of Isoetes . 
255 
EXPLANATION OF FIGURES IN PLATES 
XV, XVI, XVII. 
Illustrating Prof. Campbell’s paper on Isoetes. 
All the figures were drawn with a Zeiss camera from microtome-sections mounted 
in Canada-balsam. 
PLATE XV. 
Fig. 1. Cross-section of an ungerminated spore, between the nucleus and the 
wall, s s 1 t starch granules ; A l, Albuminous granules. Chromic acid, saffanine 
preparation, x 650. 
Figs. 2 and 3. Two sections through the nucleus of the same spore as Fig. 1. 
n } nucleolus. 
Figs. 4 and 5. Nuclei of spores that have lain in water, showing the first changes 
in the nucleus. Chromic acid, gentian- violet, x 650. 
Fig 6. The primary nucleus undergoing division. P } the cell-plate. Chromic 
acid, gentian-violet, x 650. 
Fig. 7. Oblique section through the apical region of a spore having 48 free 
nuclei, x 300. 
Fig. 8. Cross-section of the apical region of a spore at the beginning of cell- 
formation. Chromic acid, gentian-violet, x 650. 
Fig. 9. A somewhat older stage, in vertical sections, x about 300. 
Fig. 10. Vertical section through the apex of the young prothallium, showing 
the mother-cell of the first archegonium (a), x 300. 
Fig. 11. A few cells from the base of the same. 
Fig. 12. Vertical section of a prothallium, showing one of the first archegonia, 
which has failed to be fertilized, x 275 (about). 
Figs. 13-17. Successive stages in the development of the archegonium. x 600. 
a, mother-cell ; n, neck-cell ; c, neck-canal-cell (Fig. 14); h, neck-canal-cell 
(Figs. 15 and 16) ; b, ventral canal-cell; 0, central cell in Fig. 14, mother-cell of 
egg-cell in Figs. 15 and 16. 
PLATE XVI. 
(The arrow corresponds to the axis of the archegonium.) 
Fig. 18. Open archegonium showing the egg-cell (0 ) ; r, the receptive spot. 
X650. 
Fig. 19. Two-celled embryo in situ, x 300. 
Fig. 20. Three-celled embryo, x 650. 
Fig. 21. Eight-celled embryo, median longitudinal section. x6oo. 
Fig. 22. An older embryo in situ, x 300. 
Fig. 23. Transverse section of young embryo. x6oo. 
Fig. 24. Median section of the embryo shown in Fig. 22. 
Fig. 25. Vertical section of an embryo of about the same age, but showing 
irregularities in the arrangement of the cells, x 300 e 
Fig. 26. Two vertical sections of an older embryo. X300. 
