COURSE OF THE BUNDLES IN THE STEM. 279 



of many Selaginellas, may, as regards development, be considered as a cauHne 

 bundle, the corners of which are composed of the sympodially united leaf-traces of a 

 single bundle. On the other hand, the Lycopodiaceous plant, Psilotum triquetrum, 

 has only a cauline bundle without leaf-traces. Also in the case of Marsilia and Pilularia 

 a similar view may be held, in common with Nageli, according to the development of 

 the bundles. In the majority of the Ferns there is an obvious connection between 

 the form and arrangement of the leaves, and of the bundles which enter them ; in a 

 number of cases, especially in those forms, to be described later, with a reticulate 

 stem-system, and one bundle for each leaf, the stem-system may be recognised as 

 being composed of the constituent leaf-traces \ But in very many cases such a 

 separation cannot be carried out according to our present knowledge without arbi- 

 trary treatment, but rather a bundle-system of varying form and complication may be 

 distinguished in the stem, from which bundles for the leaves are given off at certain 

 points. The following description must accommodate itself to the facts : in each 

 case those stem-systems, which may arbitrarily be recognised as being composed of 

 leaf-traces, will be associated with those with which they correspond most closely in 

 their real structure. 



There may accordingly be distinguished on the one hand the types of Equi- 

 setum, Osmunda, Isoetes, on the other the various series of types of the Ferns, which 

 are connected by numerous intermediate forms : under the latter the Lycopodiums 

 and Selaginellas may be ranged as peculiar instances, and are here co-ordinated 

 merely for synoptical reasons. 



Sect. 74. Equisetum-. The weak bundles of the stem are arranged in a ring 

 separating the pith and cortex. From the median line of each tooth of the leaf- 

 sheath one bundle enters the stem, it here passes perpendicularly down one inter- 

 node, and then divides, at the next lower node, into two short shanks, each of which 

 affixes itself on the nearest lateral bundle which here passes out. Where the 

 number of teeth of successive sheaths is the same the bundles of successive inter- 

 nodes alternate as they do. 



Sfxt. 75. Osmundaeese ^ Comp. Figs. 128-130. The mature rhizome of 

 Osmunda rcgalis has leaf-insertions arranged with a divergence of y^, and short 

 internodes. Its centre is occupied by an irregular bluntly five-cornered prism, with 

 a thickness of about 6'"™ in strong specimens : this consists of. a vascular- bundle- 

 cylinder (Ring), a narrow sheath of delicate-celled parenchj-ma surrounding the 

 latter, and a parenchymatous pith surrounded by the ring of bundles, and with brown 

 sclerenchymatous cells scattered through it. The prism is enclosed by a cortex 2-5™'" 

 in thickness, which is dark-brown and sclerotic, but contains much starch : this 

 is traversed by vascular bundles, also surrounded by a thin sheath of delicate 

 parenchyma, on their oblique upward course from the ring into the leaves (Fig. 128). 



' .See HoUe, Botan. Zeitg. 1875, p. 265, &c. 



^ Nageli, Zeitsch. f. wiss. Bot. 3. p. 143; Beitr. /. r. p. 57. — Cramer, in Nageli und Cramer, 

 Pflanzenphys. Uiiters. Heft 3, p. 21. — Hofmcister, Vergl. Unters. p. 93. — Duvaljouve, Hist. Nat. des 

 Equisetum de France, J 864. 



^ Giippert, Flora, 1848, Taf. IV. A. — Unger, Uenkschr. d. Wiener Academie, Math.-Naturwiss. 

 Classe, Bd. VI (1853).— Milde, Monogr. Osmundse, p. 32. 



