COURSE OF THE BUNDLES IN THE STEM. 261 



Some of the Rhipsalidem ^ have round stems, others angular and winged ; both forms 

 have in transverse section a circular or elliptical ring of bundles, which, especially in 

 the winged species, is surrounded by a very broad succulent cortex. In the round 

 forms, such as R. Saglionis, salicornioides, the one-bundled leaf-traces pass slightly 

 obliquely downwards through the cortex into the ring, which is originally formed from 

 them alone, but later secondary intercalary bundles also appear (Chap. XIV). In the 

 winged forms the leaves are seated only on the angles. The bundles of the trace enter 

 these, and run, in the inain tangentially-perpendicular and radially-oblique, down 

 through the cortex ; they enter the ring about the level of the next lower leaf, and 

 then descend further in a perpendicular direction. They thus form the portions of 

 the ring corresponding to the angles. But the portions of the ring between these, 

 which correspond in the elliptical ring of two angled forms (e. g. Lepismium radicans, 

 Rhipsalis carnosa), to the broad sides of the ellipse, as seen in transverse section, and 

 which comprise the greater part of the ring, are here composed of cauline longitudinal 

 bundles, connected here and there by oblique anastomoses: on these the common 

 bundles insert themselves in the region indicated. These cauline bundles correspond 

 to the secondary intercalary bundles, which complete the woody ring of typical Dicoty- 

 ledons, and which will be described in Chapter XIV; but they are distinguished from 

 these by their appearing on the first primary differentiation of tissues. Finally, in all 

 Rhipsalidea: branches come off from the bundles of the trace during their course through 

 the cortex : these with their further branches form a cortical network of bundles (which 

 is further strengthened by the bundles which come from the axillary buds). The 

 special form and development of this varies according to the species, in the winged 

 species it is exclusively or chiefly expanded in the wings, in a radial direction. Compare 

 Vochting, I.e. 



It is not known how far other Cactace9e, which are winged and have a cortical net- 

 work of bundles, correspond to the winged Rhipsalidea; in the course of the bundles 

 of the leaf-trace and intercalary bundles. 



III. The Type of the Palms. 



Sect. 64. The stem of most Monocotyledons does not show the bundles 

 in the transverse section of an internode arranged in a simple ring, but within 

 a peripheral zone of cortex, which has no bundles, there is a circular surface, in which 

 either several cc/centric irregular and interlocking series of bundles are arranged 

 round a central portion without bundles (pith), as e.g. in many stems of Grasses, 

 which later become hollow ; or the bundles lie scattered over the whole surface. 

 Thus instead of the ring of bundles of the Dicotyledons there is here a cylinder, 

 which contains the bundles ; the zone surrounding the cylinder, which was called 

 the cortex, corresponds to the cortex of the Dicotyledons : the terms pith and 

 medullary rays may be used in a comparative sense for the bands of other tissue 

 (as a matter of fact parenchymatous) which lie between the bundles in the cylinder. 



The arrangement of the bundles in transverse section in the Palm type depends 

 upon the radially-oblique course of the leaf-traces. This must first be demonstrated 

 for that form which may be called the simple Palm type : with this are further 

 connected a number of more or less divergent phenomena. 



' Vochting, Moipholog. und Anat. d. Rhipsalideen, Pringsheim's Jahib. IX. p. 326. 



