EXPLANATION OF THE FIGURES. 483 



PLATE LV. 



SELAGINELLA HOKTENSIS. 

 FIG. 



1, 2. Longitudinal section through that part of the naked end of a young 

 fruit-spike, at which a sporangium is going to be formed, x 500. 



3. A very young sporangium in longitudinal section, x 600. 



4. A more developed sporangium (destined to form large spores), together 



with the leaf above it, cut through longitudinally, X 400. 



5. Longitudinal section of a more developed sporangium, X 150. 

 5*. A portion of the same specimen, x 300. 



6. Longitudinal section of a large sporangium, whose mother-cells are begin- 



ning to isolate themselves, x 300. 



7. Mother-cell of large spores, which has just divided into four special-mother- 



cells, surrounded by some of its abortive sister-cells, X 400. 

 8 — 10. Double pairs of very young large spores, still slightly held together by 

 the last remains of the dissolved special-mother-cells. Fig. 8, X 300 ; 

 figs. 9 and 10, X 500. 



11. A young spherical capsule from the outside ; through its walls the four 



spores, already of a considerable size, are just visible, X 30. 



12. A slightly more developed spherical capsule, opened by a longitudinal sec- 



tion, X 50. 

 12 d . One of the spores of the latter, after long soaking in water, X 300. 



13. A somewhat more developed large spore, x 300. 



14. Transvere section of a more perfect large spore, X 300. 



14*. The same spore treated with a solution of caustic potash. The exosporium 

 is not shown. 



15. Half-ripe spore, X 50. 



16. Fragment of the wall of a ripe spherical capsule, in longitudinal section> 



X 200. 

 16*. A fragment of the latter wall, seen from the outside. The boundaries of 

 the larger cells of the second inner layer are just visible through the 

 small ones of the upper surface, x 300. 



17. Fragment of the membrane (the inner and the outer) of a ripe large spore, 



cut through longitudinally, x 500. 



18. Mother-cells of small spores. The lower one still exhibits the primary 



central nucleus ; in the upper one to the right it is already dissolved ; in 

 the upper one to the left are four daughter- nuclei, X 300. 



19. A similar mother-cell which has just divided into four special-mother-cells, 



X 300. 



20. A set of four mother-cells arranged tetrahedrically, in each of which a spore 



is just forming, x 300. 



20*. A similar specimen. The special-mother-cells are placed decussately. 



2L First rudiment of a leaf (part of an especially successful longitudinal sec- 

 tion of a leaf-bud), X 600. 



22, 23. The stages of leaf-development following next after fig. 21, in longitu- 

 dinal section, x 600. 



24, 25. Fore-ends of young leaves seen from the surface, X 300. 



