COURSE OF THE BUNDLES IN THE STEM. 283 



Other species of the genus show a different arrangement of the bundles in the stem, 

 Such as ' 2 median, 3 median, 3 forming a triangle, or numerous scattered bundles '.' 

 S. insequalifolia shows three median ones (Fig. 131). S. Lyallii has in its strong main 

 shoots, which emerge above the ground, ten or twelve bundles distributed in the trans- 

 verse section in three parallel equidistant rows in an almost quadratic surface ; where 

 the number is ten they are so arranged that three roundish ones form two opposite 

 sides of the quadrangle, while one transversely extended one occupies each of the t«o 

 other sides, and two other roundish ones lie in the middle of the quadrangle and 

 form, with the two transversely extended ones, a row of four parallel to the rows of 

 three. Other transverse sections of the same shoot show in place of one of the 

 transversely extended bundles two contiguous round ones, which are doubtless products 

 of its division. The course of the bundles and tihe insertion of the bundles of the 

 leaves have not as yet been investigated in those shoots which have other than one 

 axile bundle or two lateral ones. In S. spinulosa, which has homomorphous leaves 

 in many rows, there is a single axile bundle of roundish transverse section (and with 

 a structure differing from that of other species) : the leaf-bundles insert themselves 

 on it on all sides. 



FiLICES AND HyDROPTERIDE^ ■^. 



Sect. 79. It has been already stated that there is always in the seedling of 

 these plants one axile bundle composed of the single, acropetally developed bundles 

 of the leaves. In many cases each lateral shoot begins with one such bundle. 



In a number of forms this structure is persistent in the mature stem. In the 

 large majority the bundle extends itself, and forms a tube, which surrounds a parens 

 chymatous cylinder of pith, and is enclosed in a parenchymatous cortex. At the 

 insertion of each leaf the tube has a gap, the foliar gap, from the margin of which 

 the bundles start, which go into the leaf; ,at other points it is closed, or reticulately 

 perforated. Of this simple bundle-tube — or ring of bundles as it appears in transverse 

 section — several special forms may be distinguished. 



In relatively few cases there are in addition to the simple tube accessory, me- 

 dullary, and cortical bundles, or there appear several concentric tubes or rings. 



a. Axile bundle and simple bundle-tube. 



Sect. 80. One axile bundle, from which a branch goes to each leaf, traverses, 

 as in submerged Phanerogams, the floating stem of Salvinia and Azolla. It occurs 

 also in the rhizomes of Pilularia minuta, exceptionally also in weak plants of P. 

 globulifera ', in the investigated stems of species of Hymenophyllum *, Gleichenia, 



' Compare A. Eraun, /. c. 



^ Mohl, Structura caudicis filicum aiborearum, &c. in Martins, Ic. Plantar, crypt. Brasil. Tab. 

 29-36, — Verm. Schriften, p. loS. — Hofmeister, Beitr. zur Kenntniss d. Gefiisskryptogamen, II. — 

 Abhandl. d. K. Sachs Gesellsch. d. Wissenschaften, V. p. 602.— Stenzel, Ueber d. Ban u. d. Wachs- 

 thum d. Fame, Nova Acta Acad. Leopold. Bd. 28.— Mettenius, Ueber den Ban von Angiopteris, 

 Abhandl. d. K. Sachs Gesellsch. d. Wissensch. IX. p. 500.— Trecul, Ann. Sci. Nat. 5 ser. lom. X. 

 p. 344, and tom. XII. p. 218. 



2 Russow, Vergl. Unters. p. 13. 



' Metlenins, Hymenophylleae, I.e. (compare above, p. 126). 



