COURSE OF THE BUNDLES IN THE STEM. 



343 



exactly it is = />. Tiie transverse section of the internode of Hydrocotyle shows, e.g. six 



alternating unequal bundles, if three enter each leaf: that of Foeniculum shows, when the 



number from each trace is equal, twelve (Fig. loi) if seven enter each leaf, and sixteen 



if nine bundles enter each leaf. As the result of inequality 



in number of successive traces in the growing plant, there 



occur also in Foeniculum deviations from the above special 



scheme. Those modifications of the course of the bundles, 



which certainly occur in the flowering shoots of the Urabelli- 



ferae in question, and in many with deviating conformation, 



have not been investigated. 



15. Leaves opposite, the pairs decussating more or less 

 exactly. The bundles of one pair pass perpendicularly 

 down through two internodes, and then curve, in the 

 second lower node, sometimes converging symmetrically, 

 sometimes both turning in the same direction, and then 

 descend further, and unite with those belonging to lower 

 leaves. This condition is plainly seen in the youngest 

 stages only, later a second shank is usually formed at the 

 point of curvature, so that the bundle becomes branched, 

 and sits astride of that directly below it (Fig. 102). 

 Further in many allied cases, the lower ending of the 

 bundles becomes quite indistinct, by their coalescing 

 laterally by means of intermediate bundles which appear 

 very early (Chap. XIV). 



To this category belong, according to Nageli and 

 Rohrbach {I.e.), Fraxinus excelsior, Vinca minor, Apocynum 

 hypericifolium, species of Phlox, Veronica incisa, Calluna -vul- 

 garis, Hypericum quadrangulum, Androsssmum, Euonymus 

 europmus, species of Alsine, Spergula, Cerastium, Dianthus 

 and Silene, also Galium and Rubia. Figs. 102 and 103 may 

 illustrate the arrangement for the special case of Cerastium. 

 Fig. 102 is the scheme for the course of the bundles of a 

 shoot with the cylindrical surface reduced to one plane; 

 ab, cd, ef, gh, are the bundles of foliage leaves, the letters 

 standing at their point of exit from the ring. Below 

 the node marked dc these bundles of the trace are alone 

 present. Above dc there are also others, viz. p, 0, n, the 

 bundles of the terminal flower-stalk, and hi, Im, of which 

 pairs one enters each of the branches in the axils of the 

 leaves g and k (comp. Sect. 94), All these bundles have a 

 place in the ring as shown in Fig. 103, which represents a 

 transverse section through the internode above ef. 



16. Leaves in whorls: traces consisting of one bundle, 

 which runs down more than two internodes. Ircvirania 

 longifolia, Russelia juncea. 



17. Leaves opposite: traces of three or four bundles, 

 which unite at the second lower node with those of the 

 next lower pair: not pectinated. Antirrhinum majus,Ruellia 

 maculata, Bignonia serratifolia, Tecoma radicans. 



18. Leaves opposite and decussate. Traces of 2 bun- 

 dles, not pectinated. Anagallis ar-vensis, Stachys angusti- 



folia, Satureja -variegata Hort. (Nageli, /. c), and many other Labiatae, Nepeta Cataria, 

 Melissa officinalis, &c. Two bundles, which are united, in the petiole to form one, 

 separate from one another at once in the stem of the Labiatae (Figs. 104 and 105), 



R 2 



Fig, 102. 



Fig. 103. 



FIGS. 102 and 103. — Cerastium frigi- 

 dum, after Nageli. Fig 102. Scheme of 

 bundle-arrangement ; explanation m the 

 text.— Fig. 103 (20). Transverse section 

 through a shoot in the internode above 

 £,yof Fig. 102. The letters indicate the 

 same bundles in both figures ; e, f are 

 already branched in Fig. 103, in the 

 sheath-like connate bases of their pair 

 of leaves. 



