qo8 PRIMARY ARRANGEMENT OF TISSUES. 



externally, at the node of the leaf which bears it, with numerous bundles, on the 

 many-bundled ring of the leading shoot, so that the pith-cylinders of the shoots of 

 the two orders are only connected by narrow medullary rays. 



The fourth category is represented by many Cactacese of very peculiar character, 



to be described below. 



A number of instances of the first and second category have been carefully 

 investigated by Nageli and others who followed him in investigating the course of 

 the primary leaf-traces ^ In those belonging to the first series, and these are the 

 most numerous, the bundle-system of the axillary shoot is united at the point of in- 

 sertion into two bundles, which may be called the bundles of insertion. These 

 affix themselves to the bundles of the trace at or immediately below the node of 

 the leaf, which bears the shoot, either — 



{a) Upon the bundles descending from above, which form the lateral limit of the 

 gap of the leaf which bears the shoot, the one being inserted on the right, the other 

 on the left — Iberis amara, Lupinus (axillary shoots of the cotyledons, Fig. 94, p. 238), 

 Passiflora Vespertilio (axillary tendrils), Antirrhinum majus, Urtica Dodartii, also 

 Pisonia ; Juniperus (Fig. 108, p. 246), and the short shoots (the bundles of needles) of 

 Pinus (Fig. no, p. 247); or (d) on the bundle or bundles of the trace of the leaf 

 itself, which bears the shoot — Anagallis arvensis (axillary peduncles). Clematis 

 (p. 245). 



In Satureja variegata both the cases designated (a) and (5) are found to occur. 

 In Galium and Rubia first the two bundles of the trace of the first pair of leaves, and 

 then those of the second pair of leaves of the axillary shoot insert themselves, usually 

 at the node, on the bundle which passes into the leaf bearing the shoot ; the same is 

 usually the case in Russelia juncea, and sometimes in Spergula arvensis. 



In the second series of cases the two bundles of the axillary shoot pass, at the 

 node of the leaf which bears it, into the bundle-ring of the leading shoot, and pursue 

 an individual course down through one (e. g. Aristolochia, Fig. 96, p. 239, Lathyrus 

 Aphaca, Figs. 98, 99, p. 240), two (e.g. Cerastium frigidum. Figs. 102, 103, p. 243), 

 and even three internodes (e. g. axillary peduncles of Viola elatior), and then insert 

 themselves on bundles of the leaf-trace. For fiirther examples and details, see 

 Nageli, I.e., and above, Sect. 61, p. 235. In the species of Galium, Rubia, Spergula,- 

 and Russelia above enumerated there is, according to Nageli, either direct insertion 

 at the node of the leaf which bears the shoot, or the bundles pursue an individual 

 course down through one internode or more. In Vitis vinifera usually three bundles 

 pass from the axillary shoot, and also from the extra-axillary tendril into the main 

 shoot, and pursue a separate course through one internode. 



The two or three bundles of insertion of the axillary shoot arise either by the 

 coalescence of the several bundles of the leaf-trace of the lowest internode to two at the 

 point of insertion, e. g. Clematis ; or these are the single bundles of the trace of the 

 two lowest leaves, e. g. Galium. 



The connection of the axillary bundle-system with that of the leading shoot is 

 however not limited to the bundles of insertion above described. According to 

 Frank's investigations ^ on Taxus, Quercus, Bidens, and Solidago, there appear con- 



Compare above, § 61. ' Botan. Zeitg. 1864, pp. 154 and 382. 



