264 PRJMARr ARRANGEMENT OF TISSUES. 



very long and thin, as e.g. in the Grasses, or egg- or spindle-shaped, as in the 

 so-called pseudo-bulbs of epiphytic Orchids, it appears otherwise at first sight. The 

 r'internode appears to be traversed by bundles, which are parallel, or convergent 

 towards both ends: of these some may be seen to enter the leaf at the node, 

 while many run into the next internode. One may however be easily convinced 

 that here also their course is such as that above described. In young stems, which 

 are still short, no variation from it is to be traced. In the subsequent elongation of 

 the internodes of the stem of Grasses to 20-50 times their original height or even 

 more, that portion of all the bundles which turns outwards while descending is so 

 elongated, that at first sight it does not appear to deviate from the perpendicular 

 in any one of the six or more internodes which it traverses : the general view of its 

 course is rendered especially difficult by a complex felt of transverse bundles in each 

 node^ (comp. Sect. 95). In the pseudo-bulbs , besides this elongation there is also 

 a transverse swelling of the internode in the middle, and a consequent curvature of 

 the bundles. 



According to the statements of Unger'' and Millardet' there is found in plants of this 

 category. Grasses, Palms, Dracaena, Yucca, Narcissus, Galanthus, Leucojum, Pandanus, 

 in addition to the bundles of the leaf-trace a further system of cauline bundles, which 

 run upwards outside the cylinder, converging towards the growing-point; accord- 

 ing to the rule which holds for cauline bundles in the Phanerogams, these are formed 

 later than the bundles of the leaf-trace. Leaving out of account the Commelinaces 

 which will be described below, and the secondary formation of wood in Dracjena, Yucca 

 and their allies, I could not convince myself of the presence of such cauline bundles, 

 which might it is true be easily mistaken for perpendicular bundles of the trace. 



As has been repeatedly stated, the cylinder traversed by the bundles is in most 

 of these cases sharply marked off from the inner surface of the cortex. The cortex 

 itself is of variable thickness, in Rhizomes it is usually of great thickness, in aerial 

 stems it is often relatively very thin. 



b. Modifications of the type of the Palms. 



Sect, 65. According to the scheme laid down in the previous paragraphs all 

 the bundles pursue an individual course up to their point of final insertion at the 

 periphery of the cylinder, this being sharply limited from the cortex, w,hich in the 

 internodes is without any bundles. 



In many cases this scheme is subject to the following modifications : (i) the 

 bundles receive oblique or transverse connecting branches, or anastomoses, during' 

 their course : (2) before they reach the periphery of the cylinder in their curved 

 course they unite with others belonging to lower leaves (Sect. 66) : and (3) cortical 

 bundles appear outside the cylinder (Sect. 67). Each of these phenomena may 

 occur separately or combined with the others. 



Anastomoses of the bundles of the leaf-trace one with another— besides those 



' Von MoH, Palmarum Structura, Tab. Q.— Schleiden, Grundziige, 3. Aufl II p ie8 



'/.^. p. 54. 



' Mem. de La Soc. des Sciences Nat. de Cherbourg, torn. XI. p. 4. 



