482 EXPLANATION OF THE FIGURES. 



BIG. 



18. Young microspores enclosed by the special-inother-cells, x 300. 



19. Half-ripe microspores after the absorption of the special-mother-cells, 



X 300. 



Figs. 20, 21. Tsoeles tenuissima. 



20. Transverse section of the stem of Isoetes tenuissima at the height of the 



lower portion of the woody mass of that species, x 20. 



21. Longitudinal section of a stem of the same species, X 20. 



Fig. 22. Isoetes setacea. 



22. Terminal bud of Isoetes setacea seen from above, x 300. 



Fig. 23. Isoetes tenuissima. 



23. Longitudinal section of a young root enclosed by the cortical parenchyma, 



together with a portion of the downward-growing wood and of the cam- 

 bium adjoining the latter. The contents of the cell of the first degree 

 and of the upwardly directed daughter-cells of the latter are shown. 

 X 300. 



PLATE LIV. 



Figs. 1 2. Selaginella helvetica. 



1. Young fruit in longitudinal section, x 30. 



2. Same section of a very young sporangium, x 300. 



Figs. 3 12. Selaginella hortensis, Mett. 



3. Longitudinal section of! he forking end of a shoot, x 30. The last fork to 



the left is a young fruit-spike. 



4. Outline of a longitudinal section of a slightly more developed fruit-spike, 



X 30. 



5. Forking end of a vegetative-shoot, the under side, x 30. 



6. End of a vegetative-shoot laid bare by a longitudinal section parallel to the 



axis ; seen from the narrow side, x 50. 

 7". Forked end of a stem, seen from the (wide) upper side, x 80. 

 7 b . The same, seen from above. 

 7 C . The same as 7", x 350. 

 7 d . The same as 7*, x 350. 

 8.. Half of an end of a shoot which has recently forked (like that shown in fig. 



5), in longitudinal section, X 500. 



9. End of a shoot at the commencement of forking, in longitudinal section, 

 X 350. 



10. A similar specimen; the fork is somewhat more advanced. 



11, ]2. Apices of shoots whose development is almost intermediate between 



those shewn in figs. 8 and 9 ; seen from above, X 350. 



