COURSE OF THE BUNDLES IN THE STEM. 



347 



bundles, these enter the hypoeotyledonary stem, which thus contains four bundles of the 

 cotyledonary trace. The epicotyledonary section contains eight bundles, four opposite 

 each cotyledon. In the cotyledonary node these eight bundles unite in pairs, each of which 

 passes down between two cotyledonary bundles, and splits within the hypoeotyledonary 

 section into two shanks, which insert themselves on the next cotyledonary bundles. 

 Below this point of union the four cotyledonary bundles unite to form the bundle of the 

 root. 



Each of the other leaves of Ephedra, which, as is well known, are scale-like, and are 

 arranged in accurately alternating whorls of two, also contains two bundles. In E. vulgaris 

 the two-bundled leaf-trace enters the ring of bundles at its own node (i) ; takes a perpen- 



FlG. 109. —Thuja plicata, after 

 Gcyler. ^ scheme of the bundle 

 system, the cylindrical surface being 

 reduced to one plane, B (16) trans- 

 verse section through ayoungshoot. 

 1. 1 the bundles, which pass directly 

 into a pair of leaves ; outside each, 

 below the surface, is a resin pas- 

 sage, h. 



Fig. no — Pinus sylvestris, after Geyler. Scheme of the 

 vascular system in the young shoot, the cylindrical surface 

 being reduced to a single plane ; leaves arranged 8/21, in a 

 ' right-handed spiral. The figures indicate the successive bun- 

 dles of the leaf-trace, which are represented as broad bands. 

 Each pair of converging bundles (represented as thin lines),, 

 near the emerging bundles — g, goes to an axillary shoot. 

 The traces unite in descending order, each with the eighth 

 lower one. 



dicular and parallel course downwards through two internodes, and inserts itself in the third 

 node laterally on the trace which emerges at node 2, each bundle joining with that laterally 

 next it. In the node there appears at an early stage a transverse girdle of tracheides, 

 which unites the bundles. Strasburger states for Ephedra campylopoda, that between 

 the two bundles of the trace, of each leaf there runs a ' complementary bundle ' which 

 arises from the girdle of tracheides : this passes through one internode, from the node of 

 the pair of leaves, to the next transverse girdle. In Ephedra altissima, according to the 

 same author, the two bundles of the trace of a leaf take a separate course only in their 

 own internode, and in the next are united to a single bundle. E. vulgaris has therefore 

 eight bundles of the trace in the internode, of these two opposite pairs belong to the same 

 pair of leaves : E. campylopoda has ten, E. altissima only six. 



The species of Gnetum have on their foliage shoots decussating pairs of leaves, separated 

 from one another by elongated internodes. Each leaf contains four or five bundles, accord- 

 ing to the species ^ According to some few investigations on Gn. Thoa the leaf-traces 

 follow the above-described scheme for the Umbelliferse. The ten-bundled trace of each 

 pair of leaves passes down through two internodes, and unites in the second node with the 



Strasburger, I.e. p, 115. 



