COURSE OF THE BUNDLES IN THE STEM. 28 1 



bundles. Slill, according to Nageli there is a relation between the corners of the 

 bundle and the insertions of the leaves. ' At some distance (about 3-8iii'») per- 

 pendicularly below each leaf one corner of the bundle projects very strongly, and 

 gradually loses itself below, but rather more quickly above. The corners of the 

 bundle are therefore the more numerous in a portion of a stem, as the vertical rows 

 are more numerous of the otherwise irregularly arranged leaves, which can only 

 with difficulty be referred to a cyclic arrangement.' 



The leaves of the Lycopodia ^ are arranged, according to the species and indi- 

 vidual, in alternating whorls of two or more members, or spirally with a divergence of 

 f, j^, Y%, &c. Each contains one thin vascular bundle. The stem is traversed by 

 one strong, almost cylindrical axile bundle, in which the symmetrically distributed 

 bands of tracheides, to be described in Sect. 107, form external protrusions, which, 

 like the bundles passing into the leaves, and the above-mentioned corners in Psilotum, 

 consist of narrow spiral tracheides, and may like them be briefl}' termed corners. 

 The bundles of the leaves insert themselves (when followed from the base of the 

 leaf) after a curved downward course through the cortex, on the corners of the 

 axile bundle. At the beginning of the differentiation of tissues, there is at first a 

 bundle of spiral tracheides at the corner, which forms a direct continuation of that 

 which passes into the leaf: it passes down through some internodes, and then 

 inserts itself on the point of curvature of one which passes out lower down. It is 

 only later that the more intci x\ masses of larger tracheides are developed. 



From these facts, and ;_(_ording to the phenomena of development, the axile 

 cylinder may be characterised as a cauline bundle, on the corners of which the 

 sympodially united bundles of the leaf-trace are directly inserted. The same facts, 

 however, admit equally well of our speaking of a polyarch (Sect. 107) axile bundle, 

 which gives off" branches from its corners into the leaves. 



The origination of the bundle which passes into the leaf follows very soon after the 

 protrusion of the young leaf itself. The development of each bundle of spiral tracheides 

 begins where the bundle inserts itself upon the point of curvature of a lower one, and 

 proceeds towards the apex of the leaf in question : then from the point of curvature it 

 proceeds again in the same direction to a higher leaf. This happens very rapidly, at 

 least in the stem itself, so that only in favourable cases (in L.alpinum) could Hegelmaier 

 find a bundle of spiral tracheides, of which the portion passing through the cortex to the 

 leaf was not already equally developed with the lower part, which passes down the 

 corner ; and Cramer ascribed to L. Selago a simultaneous development of the whole 

 bundle from its lower point of insertion to the apex of the leaf — while Hegelmaier found 

 a basipetal direction of development in the leaf itself. 



The corners of the axile bundle, as also the rows of leaves, differ greatly in number in 

 different species, individuals, and shoots of different rank of one individual, and correspond 

 to one another as a rule neither in number nor arrangement in one and the same shoot, 

 while apparently the correspondence is less close the greater the number of both. It is 

 true Hegelmaier found a correspondence of both in 75 per cent, of the last branchings of 

 L. alpinum which are covered by four rows of leaves in decussating pairs, and in about 

 60 per cent, of the branches of L. complanatum. But in most cases the number of 



' Nageli, Zeitschr. f. wiss. Bot. Heft 3 and 4 p. 132. — Cramer, in Nageli und Cramer, Beitr. 

 Heft 3. — Hegelmaier, Botan. Zeitg. 1872. p. 789, &c. — Sachs, Textbook, 2nd Kng. Ed. p. 468. 



