420 PRIMA RV ARRANGEMENT OF TISSUES. 



including the bundles, recurs in numerous Dicotyledonous stems : Caryophyllese, e.g. 

 Silene catholicLa, SaururcK, Podophyllum, species of Thalictrum (also in the petiole), 

 Papaver, Plantago, Trientalis, Hypocha^ris radicata, &c. ^ 



The converse case, that a continuous layer of sclerenchyma supports the whole 

 inner side of the ring of vascular bundles, is rare in Dicotyledonous stems. This is 

 the case in woody Piperace^ — Artanthe, Chavica spec. ^, and is especially characteristic 

 in the shoots of Bougainvillea spectabilis. 



In tough firm organs, longitudinal fibrous strands, which are not distributed 

 in the hypoderma, and which in the whole or a part of their course stand in no direct 

 relation to the vascular bundles, are more frequent than continuous annular layers. 

 Examples of this are aftbrded by the cylindrical or prismatic strands in the 

 parenchyma of the leaf and petiole of Marantaceae, Palms, Dracaenae, and Pandanus, 

 which, as regards their position, are connected with the hypodermal strands by various 

 transitional forms ; e.g. the strands in the interior of the leaf of Welwitscnia (Fig. 187), 

 and in the cortical parenchyma of Ephedra, the strands in the internodes of many 

 Potamogetons, mentioned at pp. 232 and 271, and represented in Fig. 171, p. 369 ; 

 the little bundles occurring in the parenchyma of the stem-cylinder of many Palms (As- 

 trocaryum, Cocos, Leopoldinia, Lepidocaryum spec. ^) between the vascular bundles 

 and those which traverse the cortex of most Palm-stems ; the numerous strands 

 in the rhizome of Acorus *, in the cortex of the root of Phoenix, Cocos spec. ^, and of 

 the Pandaneae, and in the axial cylinder of thick roots of the same (comp. p. 361) and 

 of the Iriarteae. 



In many of the cases mentioned, the fibrous strands have an isolated course, 

 without connection with the fibres accompanying the vascular bundles ; e. g. in the 

 roots mentioned, in Ephedra and Welwitschia ; also in the leaves of Draca&na, as far 

 as my experience goes. 



The leaf of D. reflexa*, as seen with the naked eye, is traversed longitudinally by 

 more than thirty nerves, of which about eighteen are stronger and darker, anastomosing 

 here and there by means of fine transverse branch lets ; these are the vascular bundles 

 lying in the middle lamella of the leaf (comp. p. 320), and paler nerves alternate 

 with them. The latter are simple small bundles of fibres. They do not lie in the 

 middle lamella of the leaf, but below the two surfaces, separated from the epidermis 

 by one or two layers of chlorophyll-parenchyma. In the interval between two vascular 

 bundles they usually lie 3-5 together (next the edge i-o), so that the total number 

 amounts to nearly fifty, which cannot all be clearly distinguished with the naked eye. 

 The smallest are only 5-7 fibres thick, the strongest contain about three times that 

 number. The bundles taper off gradually and terminate below the apex of the leaf, 

 and immediately above its base, and do not anastomose. Nor did I see them enter 

 the cortex of the stem. In the case of other fibrous bundles, the anatomical relation 

 to the sheaths of the vascular bundles still needs investigation. As regards those of 



* Compare Schwendener, /. r., p. 143, and the references in the notes, pp. 248-250, 



* Sanio, Botan. Zeitg. 1864, p. 214. 



' Von Mohl, Palm. Structura; Verm. Schriften, pp. 155, 170. 



* Van Tieghem, Struct, des Aroidees, i.e. 

 ^ Von Mohl, Palm. Struct, p. xx. 



^' The determinalion of the species not quite certain. 



