468 EXPLANATION OF THE FIGUItES. 



FIG. 



10 4 - Transverse section, of the same portion of the same vascular bundle, one 

 line and a half further back. The number of the cells has considerably 

 diminished during the thickening of the walls of those which remain. 

 X 150. The vessels are figured as they appear under a moderate 

 magnifying power, the sections not being very thin. 



11. Two vessels and the neighbouring cells of a complete vascular bundle seen 



in a very delicate transverse section, x 500. 



12. Longitudinal section of the margin of a principal vascular bundle, at 



the place where the thickening layers begin to appear in the spiral 

 vessels, X 500. 



PLATE XXXI. 



PTERIS AQUILINA. 



1. Similar longitudinal section of a more advanced vascular bundle, in which 



the thickening layers of the scalariform vessels are seen, x 200. 



2. Apex of the stem seen from above, x 300. 



3. Apical aspect of the apical region of the stem exposed by a transverse section 



passing through the surrounding cortical substance, which has the form 

 of a circular wall. The radiating light spots indicate the course of the 

 cortical vascular bundles which converge towards the punctum vege- 

 tationis. X 30. 

 3*. The apical surface of this end of the stem. The apical-cell is seen in the 

 middle; on the left hand, near (and above) it is the rudiment of the 

 youngest frond, x 300. 



4. Longitudinal section, perpendicular to the horizon of the end of the 



stem, x 300. 



5. The same in a longitudinal section parallel to the horizon, x 200. 



6. Horizontal section of the end of a stem which has passed transversely through 



several rudimentary roots ; that shown by the letter a is exactly 

 in the punctum vegetationis. x 5. 

 6*. The above rudimentary roots, x 200. 



PLATE XXXII. 

 Figs. 1 — 3. Pteris a^uilina. 



1. Longitudinal section of the end of a stem. At the vascular bundle, to the 



left, is the rudiment of a root laid bare, for its whole length. X 15. 

 I s . The rudiment of a root just mentioned, x 300. 



2. Longitudinal section of the very young frond of a seedling one year and a 



half old. Above the scale is the rudiment of a bud. X 250. 



3. Longitudinal section of a one-year-old frond of a full-grown plant. A 



dormant adventitious bud is laid bare. xlO. 

 3 5 . The adventitious bud, X 200. 



