EXPLANATION OF THE FIGURES. 479 



FIG. 



11. A spermatozoon enclosed by its mother-cell, set free by the crushing of a 



spore. 



12. Spermatozoon still partly sticking in the mother-cell, killed by iodine. 



13 — 15. Free spermatozoa in motion. In fig. 14 the spermatozoon drags along 

 a small vesicle at the thin end. 



16, 17. Spermatozoa killed by iodine. 



18, 19. Archegonia, just impregnated, cut through longitudinally, with two- 

 celled rudiments of embryos. Seen from the narrow side. X 400. 



20. A similar preparation ; in the lower cell of the embryo-rudiment division is 



commencing by the appearance of two nuclei, x 400. 



21. The apex of a prothallium cut through longitudinally, with one abortive and 



one impregnated archegonium, which latter encloses the four-celled 

 rudiment of an embryo, x 300. 



22. The last-mentioned embryo detached, and seen from the hinder surface. 



The line a b is parallel to the section through the impregnated arche- 

 gonium. 



23. An impregnated archegonium laid open by a longitudinal section parallel to 



the front surface of the enclosed embryo. 



24. Longitudinal section of an embryo; the number of its cells is less than in 



the preceding figure, but the characteristic extension of the apical cells 

 of the primary axis has already commenced. 



PLATE XLVII. 



ISOETES LACUSXRIS. 



1. A more advanced embryo, cut through longitudinally, X 300. 



2. Longitudinal section of a still more advanced embryo, x 200. 



3. Longitudinal section of a germ-plant three months old. The apices of the 



first and second fronds and of the first root are omitted in the figure. 

 X 200. 



PLATE XLVIII. 



ISOETES LACTJSTRIS. 



1. Lateral view of a six-months-old germ-plant, x 3. 



2. Longitudinal section at right angles to the larger transverse axis of the 



stem of a four-months-old germ-plant, x 200. 



3. Longitudinal section of the stem at right angles to the lateral surfaces of 



the woody mass of a germ-plant about eight months old, x 200. 



4. Transverse section of a one-year-old plant at the height of the terminal bud, 



X 30. 



5. Transverse section of a two-year-old plant at the place of junction of the 



upper and lower portions of the woody mass, x 10. 



6. Transverse section of an abnormal, three-furrowed, about six-years-old, stem 



of Isoetes lacustris at the same place of junction. Natural size. 



7. The middle part of the same preparation, X 30. 



8. The terminal bud of the same individual seen from above, X 300. 



