COURSE OF THE BUNDLES IN THE STEM. 289 



Polypodium and Acrostichum axillare. show numerous intermediate forms between 

 these and the simple scheme with upper and lower bundles. For further details 

 cf. Mettenius, Angiopteris, p. 552, &c., Taf. VII-X. 



i. Several concentric rings of bundles. 



Sect. 84. A number of Fern-stems with leaves in many rows — species of Pteris, 

 and Saccoloma, Marattiacese, Ceratopteris — show in the transverse section of the 

 stem several concentric rings of bundles, similar to one another in form and thick- 

 ness. As far as is known, these cases are connected with those forms above described, 

 in which the bundles running from the ring to a leaf pass gradually, and for a long 

 distance obliquely -upwards through the cortex, and are connected by anastomoses 

 both one with another, and also with those belonging to neighbouring leaves. The 

 middle of the stem is traversed by one axile bundle, or in most cases by a relatively 

 narrow tube of bundles, surrounding a narrow pith. 



From these inmost bundles there arise at regular distances, and in close relation 

 to the arrangement of the leaves, flattened or narrow bundles, which branch out at 

 once into broad reticulate layers : these do not pass out directly into a leaf close to 

 their point of origin, but run upwards and towards the surface of the stem through a 

 nunaber of internodes, and finally pass out into leaves, or divide into branches, which 

 pass out in succession. Each of these layers of bundles has the form of a portion 

 of the surface of a cone, which widens upwards : each is surrounded by a layer of 

 similar form (and a zone of parenchymatous cortex separating it from the latter), 

 and arises at its lower end from the inmost bundles. At the points of insertion of the 

 leaves there are anastomoses between the successive zones, i. e. between those which 

 are passing out, and the next inner ones, which run further. The rings which appear 

 in the transverse section are the transverse sections of the conical zones : their 

 number in any given transverse section depends upon their special course, particularly 

 upon the inclination of the conical surfaces, which is closely connected with the 

 elongation of the internodes. 



The simplest case occurs in Pteris elata van Karsteniana, and P. podophylla Sw.'; 

 also in P. Orizabae, and P. gigantea^. In the two first-named species there Is, according 

 to Mettenius, a second narrow bundle-tube within an outer one, the former being split 

 sometimes on one, sometimes on two sides. Portions of the latter curve directly out- 

 wards into the leaves ; portions of the first, turning outwards, enter the gaps formed by 

 the passing out of a portion of the outer ring, and coalesce with the outer tube, 

 which rises laterally from the base of the leaf. 



: In Saccoloma inaequale there is a similar arrangement (Mettenius). Saccoloma adian- 

 t'oides' shows in transverse section (Fig. 137) at least three closed or split rings repre- 

 senting so many conical zones, of which the outermost alone gives off broad and flattened 

 concave portions into the leaves (closely arranged with ^^ divergence) ; the middle one, 

 curving outwards, enters the gaps thus formed ; finally the inner one fills up in the same 

 way the gaps made in the middle one by this outward curvature. 



1 Mettenius, Angiopteris, p. 535, Taf. VI. 12-16. 

 ^ Karsten, Vegetationsorg. d. Palmen, I.e. p. 193. 



^ Mettenius, /. c. p. 531, Taf. VI.— Karsten, /. c. p. 194 (Dicksonia Lindeni). 



U 



