268 PRIMARY ARRANGEMENT OF TISSUES. 



bundles of the trace cannot still be distinguished in the ring. More rarely there are in 

 the sheathing leaf in addition to the two lateral bundles two other smaller bundles 

 placed symmetrically in the posterior half, near to the median line of the sheathing- leaf. 

 There was found in one case in the transverse section of the internode, in the centre of 

 the anterior side and outside the ring, a small isolated bundle, the origin and course of 

 which remained doubtful. 



The terms anterior and posterior are in all cases to be understood here, so that the 

 side next the scutellum is the posterior. 



In conclusion, a short connected description may here be given of the peculiarities of 

 the bundle-system in the Aroideae and Pandanaceae, so often alluded to above \ 



A number of forms do not diifer from the Palm type, except in the fact that in many 

 of them the bundles run for a long distance in the cortex before entering the cylinder. 

 A second category is distinguished from the first by the bundles being united on their 

 descending curved course within the cylinder, and at a considerable distance from its 

 surface. In transverse sections therefore there are found within the peripheral layer 

 • compound ' bundles, i. e. such as are cut through at the points of coalescence or separa- 

 tion. Finally, in a third group the bundles are not only united on their entry into the 

 middle of the cylinder, but are connected by anastomoses in all directions, and in such a 

 way in specially good cases that, as in the Nymphaeacese (p. 352), there is close beneath 

 the growing-point a complex network, which branches in all directions, and takes up the 

 leaf-traces as they enter, so that the typical bundle system can only be recognised by 

 slight indications. 



To the first category belongs in the first place the rhizome of Acorus gramineus and 

 A. Calamus : the majority of the bundles descend obliquely, as in the above-mentioned 

 Cyperacese, through several internodes in the thick cortex, and this, as is especially well 

 seen in A. gramineus, is traversed by bundles arranged in several rings in transverse sections. 

 Further a number of epiphytic forms with elongated internodes belong here : all the 

 Monsterineae investigated by v. Tieghem (species of Heteropsis, Monstera, Raphidophora, 

 and Scindapsus), with bundles of the trace, which sometimes enter the leaf at once at the 

 node, but for the most part traverse the cortex through two internodes before passing 

 into the leaf: further the investigated species of Anthurium and Pothos, in which also 

 cortical bundles are present, which vary in number and distribution according to the 

 species, with the exception of A. Miquelianum, which belongs to the simple Palm type. 

 The second category is connected with the above forms by the investigated species of the 

 genus Philodendron. As in the former, some of the bundles traverse the cortex through 

 (two) internodes before they pass out into the leaf. In Ph. micans all the bundles take 

 an individual course through the internodes, and are only united at the nodes, the joint 

 bundles then pass downwards, and end at the periphery of the cylinder. In other species 

 (Ph. Rudgeanum, hastatum, tripartitum) the points of coalescence are within the 

 cylinder in the internodes also, so that the transverse section often shows ' compound ' 

 bundles side by side with simple ones. According to v. Tieghem this arrangement is 

 found, subject to many modifications according to the elongation of the internodes, the 

 presence or absence of cortical bundles, &c., and specific peculiarities, in all investigated 

 Aroideae with moderately elongated internodes and unisexual flowers (species of Homa- 

 lonema, Aglaonema, Dieffenbachia, Syngonium, and others to be named below), and of 

 those with bisexual flowers in Calla palustris, Lasia ferox, and Spathiphyllum. To this 

 series belong also the stems of the Pandanea: (Pandanus javanicus, pygmaeus). The thick, 

 cylindrical (Alocasia), or almost tuberous stems, with short internodes, of other unisexual 

 Aroideae, Alocasia odorata, Colocasia antiquorum, Caladium esculentum, Dracunculus, 

 Arum, Richardia aethiopica, &c. belong to the third category, since their bundles are not 



' See van Tieghem, /. c. 



