COURSE OF THE BUNDLES IN THE STEM. 26^ 



which arise through the insertion of bundles which go to the branches and roots — 

 occur in the greatest abundance^ so as completely to mask the typical course 

 of the bundlesj in the tuberous stems of certain Aroidese to be described below. 

 In other stems with short or slightly elongated internodes they appear as an 

 unimportant phenomenon which occurs occasionally. They are however numerous 

 and characteristic in the greatly elongated internodes of the flower-stems and 

 foliage shoots of many Cyperacese, Scirpus palustris, lacustris, and their allies, 

 of Papyrus, species of Cyperus, and of Pontederia cordata \ These ' halms ' have 

 this peculiarity, that their longitudinal bundles are connected in a reticulate manner 

 one with another by small horizontal or oblique branches, like those of the foliage- 

 leaves of Monocotyledons (Sect. 91). The transverse branches run in the dia- 

 phragms (but not by any means in all), which separate the air-cavities one from 

 another. According as the longitudinal bundles are scattered over the whole 

 transverse section of the halm, or (as in Sc. palustris and its nearest allies) only form 

 a ring inside the chlorophyll-parenchyma of the cortex, there are found also 

 transverse branches throughout the whole thickness of the halm, and in the most 

 various directions, or only in the zone occupied by the ring. 



Sect. 66. The phenomenon of insertion of bundles of the leaf-trace during 

 their curved course through the middle of the cylinder, and before they reach its 

 periphery, on others which emerge lower down, and of their further descent in union 

 with the latter, is also of frequent occurrence in the Aroideae to be described below. 

 Further it occurs in Pandaneae ^ Bromeliacese (Ananassa, Tillandsia acaulis, Hort.), 

 and apparently also, according to Karsten^, in many Palms, especially IMartineza 

 aculeata. Whether this union of their course follows definite rules for certain bundles 

 of a leaf-trace remains for more exact investigation to decide. 



Sect. 67. The cortex is free from vascular bundles in many of the Monocotyle- 

 dons of this category, if those bundles be disregarded which pass to the leaves at the 

 nodes, and those which enter branches and roots : such bundles must appear in all 

 or alm.ost all transverse sections where the internodes are very short. On the other 

 hand a special cortical system of bundles may be distinguished from the cylinder in 

 certain cases. This consists in the simplest case of bundles of the leaf-trace, which 

 after their entry into the stem descend first in the cortex through one or several 

 internodes, and then enter into the cylinder. This is the case in stems of certain 

 Aroidese, in many Rhizomes, as Carex hirta (but not in C. disticha), where all 

 bundles run through one internode in the cortex : Scirpus lacustris, Typha, Sparga- 

 nium, &c. In other cases however it consists of bundles, which do not take part, or 

 at least not directly, in the construction of the cylinder : Palms, Scitamineae. and 

 many Bromeliacese. 



In the cortex of those Palms which have been investigated, small bundles, 

 which are arranged in irregular concentric rings, are found in the cortex, outside the 

 dense periphery of the cylinder. P. INIoldenhawer has compared the region in which 

 they lie with the bast of Dicotyledonous trees (Chap. XIV), Mohl has named it the 



■5 Duval- Jouve, Diaphragmes vasculiferes, /.c. ; compare p. 216. 

 * Van T ghem, Ann. Sci. Nat. 5 ser. torn. VI. p. 195. 

 ' Ka-^ ,.i, Veget, Org. d. Palmen, p. 98. 



