PHANEROGAMIA : AXIAL ORGANS. 



245 



rising in undulating lines), into the bark, describing an arc somewhat 

 convex upward and towards the interior ; these vascular bundles do not, 

 however, pass directly into the leaves, or leaf-scales, but first compose, 

 parallel with the periphery, arcs of vascular bundles, running horizontally: 

 from these, distinct vascular bundles branch off for the leaves. The very 

 unimportant materials at my disposal did not allow of my extending 

 my observations further. 



C. MONOCOTYLEDONS. 



The most simple plants of this division have no vascular bundles, as, 

 for instance, IVolffia : those nearest allied amongst the Lemnacece first 

 exhibit definite indications of these ; in Spirodela we even find them 

 combined with spiral vessels, but distributed in a plain surface as the 

 necessary accompaniment of a flat stalk. Many of the Najadece, as, for 

 instance, JVajas, Zanichellia, Ruppia, have only a central vascular bundle. 

 In the remainder we meet with the following modifications : 



1. Developed Internodes. 



The stalks and stems have always several rings of vascular bundles 

 (fig. 158. d), which occasionally enclose a pith, where a circle of vascular 

 bundles are connected by a ring of thickened parenchyma. This is often 

 the most external (usually) (fig. 158. c\ often a more internal one, as in 

 Pothos. A portion of the vascular bundle passes through the nodes into 



158 



159 



the leaf, whilst a part rises into the next internode (fig. 159. d). Small twigs 

 branch off from all the vascular bundles that pass through the nodes, 



mains of the scales of the bud : the one to the right only for the terminal bud of the 

 preceding year ; to the left for this, and also for the axillary bud, from which the 

 branch has arisen, h, A leaf at the one year old portion of the stem, together with the 

 adhering vascular bundle, i, Base of the leaf on the second year's portion of the stem, 

 with the vascular bundle appertaining to it. k k, Wood of one year's growth. 



158 Ruscus aculeatus. Transverse section of the stalk, a, The epidermis, b, The 

 bark, c, A ring of thickened cells, by which the external vascular bundles are connected 

 into a continuous zone, and thus separate the pith and bark, d, Vascular bundles scat- 

 tered through the pith. 



159 Zea Mays, natural size. A section made lengthwise through a macerated portion 

 of the stalk, a, The leaf. 6, The axillary bud. c, Adventitious root, d, Vascular 

 bundles, in their course from below upward : they give one branch to the leaf, and 

 another, or several, to the nodal plexus (e), and to the bud (6). 



R 3 



