346 



PRIMARY ARRANGEMENT OF TISSUES. 



FIG. 107 (20). — Clematis Viticella. 

 Transverse section through a young 

 internode ; further explanation in 

 the text. 



A 



that from the two cotyledons four bundles of the trace pass down into the hypocoty- 

 ledonary section. 



In all investigated cases the bundles of the trace of the first epicotyledonary leaves 



insert themselves on the cotyledonary bundles at or close below the cotyledonary node. 



With the single exception of Ginkgo, the trace of foliage and scale leaves passing 



through the stem is in the Coniferae a single bundle ; and this is 



still the case even where the leaves have several bundles, and where 



these arise, as in Dammara and the broad-leaved Araucarias, by 



splitting of the single bundle of the trace while still in the node. 



In the investigated species of Juniperus, Frenela, Cupressus, 



Callitris, Libocedrus, Thuja gigantea Nutt, Chamaecyparis eri- 



coides Hort., the leaves are arranged in two- or many-membered 



alternating whorls. Their traces consisting of a single bundle 



descend undivided through one internode, and fork about the 



middle of the second internode into two shanks, which insert 



themselves right and left upon the bundles of the trace of this 



internode (Fig. 108). 



Thuja occidentalis, Th. plicata, and Biota orientalis have' on 

 the other hand, it is true, the same whorls of two alternating 

 leaves as their nearest allies above named; but the opposite 

 traces of each pair of leaves pass perpendicularly downwards 

 through two internodes without dividing ; they then curve over 

 the leaf-trace, which emerges at the 2nd lower node, both turn- 

 ing in the same direction (more rarely converging symmetrically), 

 and affix themselves laterally on the bundles which emerge at the 

 2nd, 3rd, or rarely the 4th lower node (Fig. 109). 



In the numerous Coniferae with spirally arranged leaves, 

 Chamaecyparis glauca Hort., Widdringtonia juniperina, the in- 

 vestigated species of Taxodium, Glyptostrobus, Cryptomeria, 

 Sequoia, Cunninghamia, Pinus in the sense of Linnaeus, Podo- 

 carpus, Saxegothea, Taxus, and Araucaria, the one-bundled leaf- 

 traces have a course corresponding in its main points to the 

 scheme described for Iberis (Fi ^. no). Each bundle descends 

 independently through a definite number of internodes, and then 

 curving towards a definite lower bundle, affixes itself laterally on 

 it, and coalesces with it further down. The number of the 

 definite lower bundle, on which it is affixed, varies according to 

 the individual case, but is constant for each single case, and 

 follows the series 2, 3, 5, 8, 13, 21, ... . The direction in which 

 the apposition on the coalescing bundle takes place, is also con- 

 stant for each individual case, and' is defined by the number of 

 the coalescing bundle, so that the apposition on the 3rd, 8th, 

 or 2 1 St lower bundle is in a descending direction, that on the 5th, 

 13th, or 34th in an ascending direction with reference to the 

 leaf-spiral (Geyler, I.e.). The same rule above described is 

 followed as regards the course of the bundles of the trace in 

 the leaves of Cephalotaxus Fortunei, Torreya grandis, and, as 

 far as at present known, of Dammara australis: these leaves 

 appear at first in whorls, but are subsequently displaced spirally. Ginkgo also belongs to 

 this category, since the two bundles of the trace, after running separately through 1-3 

 internodes, unite to one, which curves in a kathodic direction above the sth lower 

 trace, and inserts itself in about the Sth lower internode in an anodic direction on the 

 5th lower trace, with which it pursues a united course in the 9-1 1 internode. 

 Among the Gnetaceee, Ephedra vulgaris has in each of the two cotyledons two vascular 



F:g. io8.~-Juniperus nana, after 

 Geyler. A scheme of the longitu- 

 dinal course of the bundles, the 

 cylindrical surface being reduced 

 to one plane ; the whorls of three 

 members are slightly displaced spi- 

 rally ; k = bundles of the buds. 

 B (16) transverse section through a 

 young shoot ; i, z, 3, the bundles, 

 which pass out in the order of the 

 figures to a whorl ; k the bundles 

 which pass into the axillary buds. 



