266 PRIMARY ARRANGEMENT OF TISSUES. 



fibrous layer. It is weakly developed in tubular stems like Calamus (Geonoma, Bactris, 

 Hyospathe, Desmoncus, Calamus), and in the cylindrical stems of Mohl (Mauritia, 

 Oenocarpus, Kunihia, Astrocaryon sp., &c.) : more strongly in Rhapis flabelliformis, 

 Phoenix, Juba^a spectabilis ') : and most fully developed in Mohl's Cocos-like stems : 

 Cocos, Leopoldinia, Syagrus, Elais, Corypha sp. Mohl regards the bundles of the 

 fibrous layer as being, at least in part, bundles of the leaf-trace, the lower ends of 

 which pass out from the cylinder into the cortex, and pass down to the base of the 

 stem as fine threads, either undivided, or split up into many thin branches (Cocos). 



More recent investigations "^ have shown that the bundles of the fibrous layer are 

 not the ends of bundles which pass through the cylinder and emerge from it lower 

 down, but that, as IMohl " also allowed to be the case with some of them, they pass 

 from the base of the leaf directly into the fibrous layer. Here they run almost 

 perpendicularly, and frequently show splittings and branchings, or fusions ; the latter 

 especially in a tangential direction, both in the internodes, and also in the insertions 

 of the leaves, so that those bundles which enter from a leaf are in direct continuity 

 with those which descend from higher leaves. Most of the bundles in question in 

 the fibrous layer consist of a number of sclerenchymatous fibres : in a strict sense 

 therefore they do not belong to this category. But in others according to Mohl's 

 figures, and according to investigations on species of Chamsedorea and Rhapis, there 

 are solitary small sieve-tubes, and in single cases also one or a few small tracheae. 

 And while some continue as purely sclerenchymatous bundles into the petiole, others, 

 after their entry into the petiole, assume the structure of fully organised vascular 

 bundles *. Further, according to a note by Schacht, there is a connection with or 

 transition to the vascular bundles of lateral roots, though the fibrous bundles do not 

 arise ' as branches ' of these. 



The cortical system of bundles of the Palms is accordingly a direct continuation 

 both of the system of vascular bundles, and of the system of purely sclerenchymatous 

 bundles in the leaves, and connects them one with another. 



Another cortical bundle-system occurs in the stem o[ Ananassa and Tillandsia 

 acaulis Hort. The parenchyma of the thick cortex is here traversed by numerous 

 bundles of the trace, which pass obliquely downwards from the leaves into the sharply 

 limited cylinder. Other thin but also complete vascular bundles pass from the base 

 of the leaf into the cortex : here they pass down, sometimes close beneath the surface, 

 sometimes deeper, but always far removed from the cylinder, through several inter- 

 nodes, and then insert themselves on one of the main bundles, and with it enter the 

 cylinder. The general direction of their course is approximately perpendicular, or 

 arched according to the dome-like shape of the end of the stem : they are besides 

 curved in a sinuous manner to a very variable extent. It is doubtful whether the 

 anastomoses of the bundles of Ananassa, described by linger^, aie these cortical 



' Wossidlo, Qusedam additamenta ad Palmaium anatomiain, Diss. Vialisl. i86o, and Nova 

 Acta Leop. Carol, vol. XXVIII. 



^ Schacht, Lehrbuch, I. p. 327. — Nageli, I.e. p. 132. — Wossidlo, I.e. 



' Palmaruni .Structura, p. xviii ; Verm. Schriften, pp. 155, 184, 



* Mohl, Wossidlo, I.e. 



'■' Dicotyledonenstamm, p. 5c, figs. 23, 24.— Anatomic imd Physiologic, p. 232. 



