208 MR R. J. D. GRAHAM ON 



has the accessory bundle been found accompanying the leaf-trace in the lower half of 

 its course. The accessory bundle, on reaching the node above that at which it 

 originates, bifurcates at the level of the vascular crescents. Each half of the accessory 

 then passes out as an additional pair of traces to the axillary bud (Plate III., fig. 20). 

 The bud supply is hence augmented by two traces ; thus in cross section with the first 

 shortened internode of the side branch six bundles appear arranged, two adaxially and 

 four abaxially. Before the bud-traces pass out to the first leaves of the side branch, 

 the accessory bud-traces fuse with them (see fig. 20). Thus the accessory bud supply 

 is shared by the two leaves. In E. altissima, E. intermedia from Kew, in E. altissima 

 from Algiers and from Montpellier, as also in E. distachya, elegantissima, lanceolata 

 from Edinburgh, the leaves of the first node of the lateral branch are in many cases 

 suppressed. This feature has been occasionally observed in other species. In correla- 

 tion with the absence of leaves, no splitting occurs in the bud supply, while the 

 accessory, when present, ends in the vascular crescents of the main axis. 



Concrescent Bundles.— This system is derived from the eight-bundle or normal 

 type by the fusion of the adjacent leaf- traces of the opposite leaf- trace pairs in the 

 second half of their course (Plate III., fig. 21, i.). At the end of its course the con- 

 crescent trace splits and the two portions link on right and left with the traces on 

 either side (fig. 21, ii.). Thus an incomplete ring is formed, interrupted only between 

 the non-concrescent leaf-traces. At the node through the formation of the girdle of 

 tracheids these non-concrescent traces become joined up (fig. 21, iii.). Thus, through 

 the ultimate splitting of the concrescent bundle vascular crescents are formed composed 

 of the same constituents as the vascular crescents in the normal type (fig. 21, iv.). 



Occasionally another type of concrescence occurs through fusion of the leaf-traces 

 in the first half of their course. Exceptionally, concrescence takes place in all the leaf- 

 traces, and the number of the bundles is reduced to four. The leaf-traces in the leaves 

 appear to be very close together in this last case. 



When there are three leaves at the node the typical vascular system is still retained. 

 If the leaf-traces be accompanied by an accessory, the number of bundles seen in 

 section is fifteen (Plate III., fig. 22) ; while if concrescence occur in the latter half of 

 the course of the bundle, the number of bundles seen is nine (Plate III., fig. 23). 



These variations due to intercalation and concrescence of bundles may take place at 

 different levels in the course of the trace, and need not be synchronous on the two 

 sides. Hence in different internodes of the same individual four, five, six, seven, eight, 

 nine, and ten bundles may be met with. Similar variations occur in those species 

 which have three leaves at the node. 



The Pith consists of large and small cells, whose walls from an early stage are 

 lignified, except around the intercellular spaces. Lignification is centripetal, being 

 found in the fourth internode of E. fragilis, v. campylopoda. The perimedullary 

 stereom (Plate II., fig. 12) has already been noticed. Cells containing tannin mucilage 

 occur in many species, though they may be entirely absent from others (Plate III., 



