343 PRIMARY ARRANGEMENT OF TISSUES. 



13. Leaves alternate, in two rows. Rows approaching one another on one side. Leaf- 

 trace of 7-9 bundles. All bundles of two successive leaves pectinated. Platanus occi- 

 dentalis. 



14. Leaves alternate, in two or more rows. Leaf-trace of numerous bundles. All 

 bundles of two successive leaves pectinated. To this type belongs Menyanthes trlfoliata, 

 with leaves in two rows, and a trace consisting of 10-13 bundles, according to Nageli: 

 also many Umbelliferae. 



According to investigations ' on ^thusa Cynapium, Phellandrium aquaticum, Hydro- 

 cotyle vulgaris, and Foeniculum officinale, the Umbelliferae of the usual form have in the 

 non-flowering shoots a bundle system, which in accordance with their similarity in ex- 

 ternal conformation is similar in its main features, though it shows individual variations. 

 The following scheme may be constructed for it (comp. Figs. 100, 10 1). The leaves are 

 in two alternating rows, or spirally arranged.: their base completely encircles the stem, 

 one margin even overlapping the other; each leaf-trace has several bundles, its width 

 being equal to the whole circumference of the stem {\) ; the leaf-trace, pectinating with 

 those of the next higher and next lower leaves, and passing downwards through two inter- 

 nodes, inserts itself in the third node on the trace which comes down from the second 

 node, and takes up in the second node the trace which emerges next above it. Each bundle 

 of the trace runs directly downwards from the node (3), in which it emerges, through its 

 internode ; it takes up in the next node (2) a bundle of the trace which comes from above 

 (3), and which affixes itself upon it; it passes in (2) between two bundles, which here 

 enter the leaf, and runs between these down to the node (i). Here turning either right 

 or left it affixes itself to one, or branching, to two neighbouring bundles, which descend 

 from node (2). Whether the junction be to the fight or left, or branched and on both 

 sides, seems to be often subject to variation. Not unfrequently the branching arises later 

 by the subsequent appearance of a second shank on a bundle originally attached on one 

 side. If the bundles of successive traces are of equal number, and their number = n, the 

 transverse section of an internode shows 2 n bundles of the trace, and of these n are 

 stronger and go to the next leaf, n are weaker, alternate with the former, and enter the 

 second leaf above. 



In the three-bundled traces of the creeping foliage-shoots of Hydrocotyle vulgaris 

 no variation from this type was observed. In other cases, with a larger number of 

 bundles of the trace, variations are frequent. They depend sometimes on inequalities in 

 the number of bundles in the successive traces, since as the strength of a shoot increases 

 the number of bundles of the successive traces enlarges, and then two or three bundles may 

 pass between two bundles of the next lower trace : sometimes on the fact that the width 

 of a trace (and leaf-insertion) is less than i of the circumference of the stem, in which 

 case certain bundles pass down through more than two internodes : sometimes there occur 

 variations independently of these, in the same species, and possibly even in one and the 

 same shoot, while many species have constant specific peculiarities. Thus the young 

 plant of Foeniculum officinale (Fig. 100) has alternating leaves in two rows, their median 

 planes diverging by 180° : the width of the leaf-insertion is i or > i of the circumference 

 of the stem, that of the leaf-trace \. The number p of the bundles entering one leaf is, 

 as in other investigated species, an uneven number: 5, 7, to 21 and more. Of the/ 

 bundles of one leaf the two marginal ones, /. /. Fig. 100, converge as they enter the 

 node (i), and unite there at once with the median bundle {m) of the next higher leaf, 

 which descends perpendicularly between them. This united bundle then descends 

 further perpendicularly through the next internode, and forks in the next node (2), close 

 above the median bundle, which passes out at that point, and each of its two shanks 

 unites with the bundle, which descends side by side with it. The course of all other 

 bundles corresponds to the scheme. The number n of the bundles of one leaf-trace 

 in an internode is thus in Foeniculum = p-i, while in cases which follow the scheme 



Carried out in i873,-in the Botanical Institute at Strassburg, by Herr von Kamienski. 



