EXPLANATION OF THE FIGURES. 465 



PIG. 



6. Longitudinal section of the fragment of a prothallium, showing an impreg- 



nated archegonium with a multi-cellular embryo which has been grazed 

 by the section. 

 C 4 . The net of cells of this embryo ; the boundaries of the cells are drawn of 

 different thicknesses, according to their age. 



7, 7*. More advanced states of 6 and 6 6 . 



8. The end of the first frond of a more developed embryo, seen from the 



surface, X 300. 



9, 10, 11. Transverse sections through the stipes of a frond of a one-year-old 



seedling 9, at the base; 10, somewhat higher up; 11, still higher. 

 X 20. 



12. 16, 17. Transverse sections through the stem of a one-year-old seedling. 



12, at the base ; 16, iu the middle ; 17, near the top. x 30. 



13. Germ-plants after the development of the frond, in longitudinal section. 



Between the first and second root of the primary axis of the embryo. 

 X 20. 



14. The top of the stem of a seedling of ten months old, seen from above. On 



the left is the rudiment of the youngest and on the right that of the 

 next oldest frond. The roundish cells, with granular contents, are 

 either mother-cells, or cells of attachment, of scales. X 200. 



15. A ten-months old seedling, in longitudinal section. The protuberance 



below on the left is the primary axis of the embryo, x 20. 

 IS. Basal outline of a young frond of a seedling, and of the scales surrounding 

 it, X 30. 



19. Upper part of the stem of a full-grown plant cut through longitudinally. 



The cellular tissue up to the vascular bundles of the divided frond is 

 removed, to show the course of the bundles. Natural size. 



20. A mesh of the net of vascular bundles of a similar stem, with the stumps 



of the vascular bundles passing from it to the fronds. X 5. 



PLATE XXVII. 



1, 2. Apical views of the ends of the stem of full-grown plants. Fig. 1 with 

 a right-handed, fig. 2 with a left-handed, cell-succession. X 200. 



3, 4. Longitudinal sections of terminal buds of full-grown plants. Fig. 3 

 X 200, fig. 4 x 170. In fig. 4, w represents the rudiment of a frond 

 divided by the section. 



5. A frond still rolled up, the scales having been removed, seen from the back, 



showing the rudiment of an adventitious bud. Natural size. 



6. Lower part of a stipes, whose lamina is already dead ; with an adventitious 



bud in process of development. Natural size. 



7. The same object, laid bare up to the vascular bundles of the cortical tissue. 



Natural size. 



8. Longitudinal section of the tip of a root, x 200. 



9. Transverse section of the same, passing through the punctum vegetationis 



at the height a b of the previous figure, X 300. 

 10. The middle region of a similar section, somewhat lower down, at the posi- 

 tion c d of the root in fig. 8, X 300. 



30 



