EXPLANATION OF THE FIGURES. 477 



PLATE XLV. 



SALVINIA. NATAXS. 

 PIG. 



1. Longitudinal section of a large spore at the commencement of germination, 



X 30. 



2. A fragment of the exosporium of a microspore, in longitudinal section, 



X 300. Three layers are distinguishable. A thin inner layer, a thicker 

 middle layer, and a very thick, apparently cellular, outer layer. 



3. A very young prothallium, detached, with a fragment of the inner spore- 



membrane adhering to it, x 200. 



4. The same, the longitudinal section passing through the entire spore, 



X 200. 



5. A more advanced prothallium, in which the first archegonium is developed; 



in longitudinal section, x 200. 



6 7- Longitudinal section of unimpregnated archegonia, in which germinal 

 vesicles are visible, x 300. 



8. Transverse section of an unimpregnated archegonium with two terminal 



vesicles. The observer is looking into it from below, and in the middle 

 of the figure the interior of I he mouth of the canal is seen. 



9. Fragment of a prothallium cut through longitudinally, in which archegonia 



are visible, one unimpregnated and the other just impregnated, x 300. 



10. Longitudinal section of the angle of a prothallium, exhibiting an archego- 



nium with an unusually long canal, X 300. 



11. Three-celled embryo, entirely filling the central cell of its archegonium. 



The position of the mouth of the canal is shown by two lines, x 200. 



12. An impregnated archegonium, with an abnormally large central cell, a small 



part of the latter only being filled by the few-celled embryo, x 200. 



13. An impregnated archegonium enclosing an eight-celled embryo, X 300. 



14 A 16-celled embryo detached, a from the outside, laterally, b in longitudinal 

 section, c seen from behind. 



15. A somewhat more developed embryo detached, a from above, b from the 



side, c also from the side turned round 90. x 20. 



16, 17, 18. More advanced embryos ; figs. 16 and 18 entirelv, and fig. 17 half 



detached. Pigs. 16 and 18 are X 200, and fig. 17 is x 300. 



19. Embryo enclosed by the prothallium, x 300. 



20. Detached embryo seen from the front surface, x 200. 



21. Embryo enclosed by the prothallium. The first leaf is beginning to develope 



itself above, x 300. 



22. Spores with prothallium and embryo somewhat more advanced, in longitu- 



dinal section, x 50. 



23. A similar embryo, x 200. 



21. A similar embryo detached and seen from the front surface of the first leaf, 

 at the lower margin of which the end of the principal axis is clearly 

 visible, X 200. 



25". An embryo more advanced, seen half in front. Near the first leaf a the 

 principal axis b which is already once forked and is in the act of 

 forking again is visible ; behind it is the hinder end of the germ-plant c. 



