2cSo 



PRIMARY ARRANGEMENT OF TISSUES. 



One bundle enters each leaf: 



the arrang 



Fij;. 12S 



Fig. 129. 



Figs. 128 and 129. — Osniunda regalis. Fig. 128. Transverse 

 section through a strong stein, seen from above, i. e. from the 

 apex of the stem ; magnified about twice, i lowest bundle of 

 leaf-trace, from which a root-bundle passes through the cortex. 

 Fig. 129. — Sketch of the bundle-ring in the former figure, 

 more strongly magnified, i. Bundle of the lowest trace cut 

 through just at its point of entry mto the ring, and with one of 

 the two root-bundles, which are here attaclied to it. The figures 

 I — t^ indicate the bundles of the trace of the thirteen successive 

 leaves, which are visible in the transverse section ; N'o. 10 is 

 abnormally united with 2 Compare Fig. 130. 



Fig. J30. — Osmunda regalis. 

 Scheme of the vascular system in 

 the stem, the cylindrical surface 

 being reduced to a single plane ; 

 arrangement of the leaves 5/13. 

 The bundles of the leaves num- 

 bered in genetic series at their 

 point of exit ; each has two roots 

 inserted close to the point of exit, 

 and indicated by short transverse 

 strokes. On 2 and 10 is to be 

 seen the anomaly observed in the 

 specimen upon which the scheme 

 is founded, \\7.. that 10 inserts 

 itself on 2 close to the point of 

 exit of the latter, instead of con- 

 tinuing its course to 2 — 5. 



ement of the bundles in the cylinder is quite 

 similar to that of the ConifercC with alter- 

 nating leaves with a single bundle (Fig. 

 1 30). From one leaf n one bundle enters 

 the cylinder, and runs almost perpendi- 

 cularly downwards, as a rule through 1 3 in- 

 ternodes, and then, when close to the leaf 

 «-i3 perpendicularly below it, it curves 

 towards the ascending side of the bundle 

 belonging to the leaf «-8, and unites with 

 it. In the cases investigated the insertion 

 and coalescence took place occasionally 

 even after a shorter course, e. g. in the 

 case of the bundle 10 in Fig. 130, eight 

 internodes below the point of exit. The 

 bundles are strongest at their point of exit from the cylinder, 

 and are of horseshoe shape. In the petiole they retain 

 this form, or are at least half-moon-shaped. In the cylinder 

 of the stem, as they pass downwards, they decrease in thick- 

 ness at first gradually, and then quickly, and assume a 

 wedge-shaped transverse section. Here they are separated 

 from one another by narrow bands of parenchyma (medul- 

 lary rays). The structure of the whole transverse section 

 (Fig. 128) may be deduced from the above description. — 

 The bundles, which pass into the first leaves of the seedling, 

 unite to an axile bundle without any pith : this gradually 

 extends into the ring of bundles surrounding the pith. 



In Todea africana and T. hymenophylloides are seen 

 phenomena exactly similar to those in Osmunda, which need 

 not be described in detail here. 



Sect. 76. While thus the bundle-system of these plants, 

 and of the Equiseta, may well be ranged under the type of 

 Dicotyledons, and is specially allied to that of the Conifers 

 (Juniperus, Widdringtonia^), the species of Isoetes have in 

 their extremely shortened tuberous stem an axile bundle 

 without pith, as is the rule in submerged water-plants : this 

 bundle is built up sympodially by the coalescence of the 

 inner ends of the one-bundled leaf-traces. Phylloglossum 

 may also belong to this category ^ 



Sect. 77. Psilotum and Lycopodium. The leafy stem 

 of Psilotum triquetrum ■■' has one vascular bundle with 2-8 

 corners which project more or less from the surface. It is 

 cauline throughout, the small leaves have no vascular 



' Compare above, p. 246, and Geyler, I.e., especially Taf. IV'. 

 * Compare Metteniiis, Botan. Zeitg. 1867, p. 98. ^ Nageli, Beitr. I.e. p. 52. 



