COURSE OF THE BUNDLES IN THE STEM. 



245 



20. Leaves opposite : traces consisting of three bundles, the lateral bundles of the same 

 pair united from the iirst. Mercurialis annua and M. perennis. 



21. Leaves opposite : traces consisting of five bundles, the two lateral bundles of the 

 same pair united from the first. Sambucus ?iigra. 



B. Gymnosperms^ 

 As has been above mentioned, the vas- 

 cular system in the stems of the Coniferae 

 does not differ from that of the Dicoty- 

 ledons : they will therefore be mentioned 

 here only as special instances of the 

 type of the Dicotyledons. 



The seedling of most of them has two 

 opposite cotyledons which grow green on 

 germination, and rise above the ground ; 

 rarely (Ginkgo, Araucaria, section Colum- 

 bea) they remain in the ground. More 

 than two occur exceptionally in many 

 genera, and constantly in Taxodium (4 

 to 9) and in the Abietinea;, in the sense of 

 Strasburger, i. e. Linnaeus' genus Pinus. 

 The number of the cotyledons differs here 

 according to the species, and varies in the 

 same species within wide limits : e. g. in 

 Abies pectinata between 4 and 7, in Pinus 

 sylvestris between 3 and 8, in Pinus Pinea 

 between 8 and 14. Discounting single 

 exceptions to be named below, one bundle 

 enters the short hypocotyledonary section 

 from each cotyledon ; where there are 

 two cotyledons both bundles run vertically 

 downwards, and soon undergo coalescence 

 to form the root-bundle : where the num- 

 ber is higher, two or three bundles coalesce 

 immediately after entering the hypocoty- 

 ledonary section to form one, so that the 

 number of the bundles of the trace in the 

 latter is smaller than that of the coty- 

 ledons. Statements by Lestiboudois {I.e., 

 pp. 25 and 26) lead to the assumption that 

 in Cupressus pyramidalis and Abies bal- 

 samea the bundle, which passes from the 

 cotyledon into the stem as a simple 

 bundle, splits at the node into two shanks, 

 and that the opposite shanks of two 

 neighbouring bundles unite into one, 

 which (alternating with each pair of coty- 

 ledons) descends perpendicularly. The 

 cotyledons of Araucaria brasiliensis ^ have 

 each 8 vascular bundles, and these each 



Fig. 106 (40).— Clematis Viticella, after Nageli. Endof abraiith 

 made transparent by removing the surface and treatment with 

 potash, showing the course of the leaf-traces. The outgoing ends 

 of the bundles are somewhat distorted by slight pressure; the 

 two highest pair of leaves a and y S have as yet no developed 

 bundles. 



unite in the cotyledonary node to two, so 



' Nageli, /.c. — Lestiboudois, I.e. —K. B. Frank, Botan. Zeitg. 1864, p. 150. — Geyler, Gefass- 

 biindelverlauf in d. Laubblattregion d. Coniferen, Pringsheim's Jahrb. VI. — Strasburger, Die Coni- 

 feren und Gnetaceen. ^ Strasburger, I.e. p. 369, 



\ 



