ANOMALOUS THICKENING IN DICOTYLEDONS AND GVMNOSPERMS. 603 



the radial bands of parenchyma of the highly parenchymatous wood, which extend 

 from the pith, the consequent splitting and disrupture first of the medullary sheath, 

 then of the outer regions of wood, the appearance of new cambial zones close to the 

 separated segments of wood, which form also new bast, and finally also the 

 appearance of new strands of wood and bast in the pith itself, which are derived from 

 secondary meristem, and have an independent growth in thickness. The changes 

 start, in the branch investigated, from a swollen portion twining round a wire and 

 exposed to strong pressure, a fact which shows that they are at all events £;dvanced 

 by mechanical causes. 



Fig. 238.— Eauliinia spec. Transverse section of a stem, two-thirds tlie naturai size, from Schieiden's 

 Grundziige. a all dotted figures are portions of wood, sometimes with remarkably large pitted vessels ; 

 c bundles of wood, conspicuous by their whitish colour, with radial medullary rays, and arranged in a simple 

 circle (probably the origmal narrow medullary sheath, split up). With exception of the circle (c) the rest of 

 the wood consists for the most part of parenchyma, and the medullary rays talce a sinuous course. The 

 bands left white {b) between and around the woody bundles are masses of parenchyma and bast. 



It is doubtless similar anatomical changes which bring about the frequent splitting 

 up of the xylem in the old stems of climbing Bauhinias ', especially of the section 

 Caulotretus^, of which the Fig. 238, which, according to Schleiden, is of a Bauhinia, 

 may give an approximate representation. In these Lianes however there is, in 

 addition to the phenomena in question, another also, which has not at all events 

 been shown with certainty to occur in other forms, viz. a long continued ^rozc/A in 

 length of the old layers of wood, which may also be ascribed for the most part 



i3.- 



' Compare Gaiidichaud, /. c. Tab. XVIII. Figs. 2, 3. 



' [See V. Hohnel, Die Entstehung der welligflachen Zweige von Caiilotretus, Pringsh. Jahrb. Bd. 



-Also, Warburg, in Botan. Zeitg. 1883, p. 617, &c.] 



