5<So SECOND ART CHANGES. 



between bast and outer cortex, a massive persistent ring of strong sclerenchyma, 

 and usually single sclerenchymatous fibres at the outer side of it. In S. brachiata and 

 toxifera there are besides large groups of strong sclerenchyma in the secondary 

 bast. The parenchymatous outer cortex forms in all of them a thick periderm 

 at the outer surface, and especially in S. innocua, a thick soft mass of cork. On the 

 structure of the wood of other species it need only be remarked, that it is dis- 

 tinguished from that of S. nux vomica by the relatively much larger quantity of 

 thick fibres, otherwise it shows no generally remarkable properties. The details 

 still require more exact investigation. In allied Loganiaceas, I found in Logania 

 longifolia and fioribunda bicollateral bundles of the leaf-trace, but normal bast, and 

 no sieve-tubes in the xylem. Gaertnera longifolia, Sykesia spec, and Fagrgea 

 Janceolata show a perfectly normal Dicotyledonous structure, and no bicollateral 

 bundles of the trace. 



Of the Dicella above-named only a few dry pieces of the stem about 5-6™!^ thick, 

 sent by Fr. Miiller, w-ere available ; some of these were round, some very eccentrically 

 developed. The round pith is immediately surrounded by a uniform ring, about eight 

 cells thick, of narrow ordinary xylem elements, arranged regularly in radial rows. 

 The other secondary wood consists chiefly of thick-walled pitted vessels and fibres, 

 with uniseriate medullary rays, partly also of masses of thin-walled tissue composed 

 of M'ide parenchymatous cells, sieve -tubes, and narrow sacs with conglomerated crystals, 

 which are marked off from the thick-walled mass by an almost unbroken layer of 

 partitioned crystal-sacs with small klinorrhombic crystals. This delicate tissue, with 

 sieve-tubes, is distributed in the thick-walled vascular tissue in the form of anasto- 

 mosing flat strands, which appear in transverse section as irregular concentric 

 segments of a ring, of very unequal size and form, often with sinuous curvature, 

 and frequent anastomoses. These form bands and zones in the transverse section, 

 which are embedded in the hard mass of xylem, and are, on the average, smaller 

 and narrower than the hard portions, which alternate with them ; these phenomena 

 give the whole transverse section a peculiar, finely banded, almost marbled appear- 

 ance. As far as* could be made out from the dry britde material, the whole mass 

 of wood described arises on the inner side of a delicate one-layered zone of cambium. 

 This is surrounded by a thin cortex, which shows no peculiarities worthy of mention, 

 beyond the fact that in the secondary zone of bast, which contains narrow scattered 

 fibres, and many small conglomerated crystals, sieve-tubes were not to be found. 



Further details of structure have been in part purposely left unnoticed in the 

 above notes, both in Strychnos and Dicella, in part they require still further in- 

 vestigation. 



Sect. 187. The appearance of a ring o{ cambium and secondary thickening on 

 the mner side of the external, normally growing ring of wood, has been discovered by 

 Sanio ' in the stem of Tecoma radicans. The bundles of the leaf- trace of the normal 

 bundle-ring'^, with the exception of those perpendicularly below the next higher pair of 

 leaves, are bounded, when young, on the side next the pith, and opposite the primordial 

 spiral vessels, by a small strand of delicate cells, which remain narrower than those 

 surrounding them. The innermost group of cells of each bundle, which abut on 



\ Botan. Zeitung. 1864, pp. 61, 228. ? Compare Nageli, Bcilr. I. p. 107. 



