410 Dr. G. Ogilvie on the Forms and Structure of Fern-stems. 



is the more probable from an arrangement precisely of this 

 kind obtaining in creeping rhizomes, such as those of the bracken. 

 It is well known to botanists that there is a similar diversity in 

 the extension of the medullary rays of Exogens : they are much 

 larger, for instance, in the oak than in most other woods, and 

 in the Clematis they reach the whole length of the internodes, 

 so that, when they decay, the stem breaks up by the separation 

 of its component woody wedges. 



EXPLANATION OF PLATES. 



Plate VIII. 



Fig. 1 . A portion of the branched and creeping rhizome of Poly podium 



Phegopteris, showing the fringe of wiry rootlets and the persistent 



bases of old leaf-stalks. 

 Fig. 2. The branched and creeping rhizome of Polypodium vulgare. It is 



more thickly set with rootlets than the last, and marked with the 



seal's of fallen petioles. 

 Fig. 3. The thchotomons caudcx of Blccluium boreule, with the axis exposed 



by cutting off, close to their origin, all the foot-stalks of former 



years' fronds. 



Plate IX. 



Fig. 4. The dichotomous caudex of a large bushy specimen of Allosurus 

 crispus, stripped of the rootlets, the petioles of former years, and 

 of most of the fronds. 



Fig. 5. The dichotomous caudex of Asplenium Filix fcemina, exposed by a 

 section aloug the axis of its several branches, to show the con- 

 nexion of the bases of the leaf-stalks of successive years with the 

 core of the stem. 



Fig. 6. Another specimen of the same species, with the caudex stripped of 

 its rootlets and petioles, the scars with which it is marked indi- 

 cating their points of attachment. Of these there must be con- 

 siderably more than a thousand : the plant had certainly upwards 

 of a hundred fresh fronds when dug up. 



Plate X. 



[Illustrations of the rhizome of Lastrea Filix mas.~] 



Fig. 7- A caudex which has been forced into an upright line of growth. 



Fig. 8. Another specimen, showing the usual horizontal direction of growth, 

 the terminal bud forming an angle with the rhizome. 

 Both these specimens are in their natural state. 



Fig. 9. Tessellated appearance of the surface of the caudex when the pe- 

 tioles are cut off close to their origin. The dots indicate the cut 

 ends of the vascular bundles going to the fronds. 



Fig. 10. Perpendicular section of an upright caudex, showing the inter- 

 rupted line on each side of the axis, where the reticulated fibro- 

 vascular cylinder has been divided by the section. The figure 

 shows also the connexion of the bases of the petioles, and a 

 lateral bud arising from one of them. 



Fig. 11. A portion of a preparation showing the netted fibro-vascular cy- 

 linder of the caudex, removed entire by careful dissection from 



