ANOMALOUS THICKENING IN DICOTFLEDONS AND GFMNOSPERMS. 607 



formations which arise in the cortex, and at first resemble the appearance of successively 

 renewed cambiums (p. 590), though, as ah-eady intimated, they cannot always be included 

 among these ; and thirdly, combinations of the two processes. 



In the old parenchyma of the root new partial cambiums appear, without the activity 

 of the normal ring ceasing : they are partly in connection with normally-formed vascular 

 bundles, partly with such bundles as have been formed from secondary meristem in the 

 parenchyma separate from the former : in both cases they independently produce new 

 secondary wood and bast in variable quantity, and with the normal succession and 

 orientation. According as this takes place, the original tissue is displaced and crushed 

 to such an extent, that finally the whole root may consist of irregularly grouped strands 

 of wood and bast irregularly lobed in transverse section : each of these has its-own ring 

 of cambium. Still further disarrangement may arise by the original normal ring of cam- 

 bium ceasing to be active, and becoming quite obscure ; and by the appearance of 

 repeated newly active layers of cambium in the partial xylem-bodies, as they did before 

 in the original xylem. These phenomena appear in various individual forms, the de- 

 scription of which would here lead us too far, e. g. in the roots of Convolvulus Scammonia 

 and Ipomcea Purga. 



In very many roots of Convolvulaceae, both in those which are perennial, and also quite 

 regularly in the annual roots of Pharbitis hispida Choisy (Ipomcea purpurea), the other phe- 

 nomenon appears: new strands forming wood and bast by means of their own cambium arise 

 from secondary meristem, in the parenchyma of the secondary cortex, immediately outside 

 the strands of bast. Their mode of origin is fundamentally the same as in the formation 

 of renewed cambial rings at the periphery of old ones that are becoming extinct. The 

 same process may also be renewed as in the latter case in successive zones lying further 

 out. A difference however from the typical process of formation of renewed cambiums 

 is found in the first place in the fact that the production on the part of the normal cam- 

 bium does not cease with the appearance of the new bundles, but continues; and in the 

 fact that, in most cases at least, closed cambial rings or segments of rings, producing 

 strands of wood and bast alternating with medullary rays, and having a normal orienta- 

 tion, are not formed by the secondary development ; but separate strands, each of which 

 has its own more or less complete circular cambium, from which is derived an increase 

 of wood and bast. 



The whole transverse section thus resembles, to a certain extent, that of a stem of 

 the Sapindaces : there is a central normal round xylem, surrounded by a number of 

 smaller ones, in simple, later also in compound series. The longitudinal course of the 

 peripheral strands is irregularly undulated ; they are frequently connected laterally one 

 with another, and with the normal xylem by anastomoses. The phenomenon described is 

 found in the permanent stems of several species. Jussieu^ describes in the case of C. ma- 

 labaricus, in a stem 8o°> thick, 8-9 irregular concentric rings, and found the same in the 

 stem of several undefined species. The same condition has long been known for the root 

 of Ipomcea Turpethum, the roots of other species show the same, and in such a way that 

 the cortical bundles appear only in the root, not in the stem. In the woody roots of the 

 red garden Convolvulus (Pharb. hispida) they are well developed, but only pass up into 

 the hypocotyledonary stem, and there pass over with thin ends into the strongly thick- 

 ened normal xylem. 



Both processes, the secondary formation of bundles in the parenchyma of the old wood 

 and in the cortex, may be combined in the Turpeth root, and in the roots which are 

 found in druggists' shops as Mechoacanna and Stipites Jalapae. In these cases the 

 secondary development of xylem-forming strands goas on, sometimes in the original 

 normal xylem, while sometimes it may extend also to the xylem-bodies in the cortex. 



As stated above '^, on p. 233, the massive starchy parenchyma of the napiform lateral 



' I.e. p. 123. 



2 P.S. L. Koch 'Verhandl. d. Naturhist. Vereins in Heidelberg, Bd. I. Heft. 4) has recently 



