^68 SECONDARY CHANGES. 



anomalies of growth, which differ from normal cases in having some other arrange- 

 ment of the initial layers which maintain growth, or some other distribution of the 

 tissues, or in showing special phenomena of dilatation. It must be maintained from 

 the first that even the anomalies to be described are derived from ordinary initial 

 structures, which are usually formed according to the normal Dicotyledonous type ; 

 that in their case also we have to do with a further formation of secondary wood 

 and secondary bast, which are derived from the same kinds of tissue as the normal 

 formations ; that their formation arises from secondary meristems and cambial layers, 

 which, when present, behave fundamentally like, or very similarly to such normal 

 tissues ; and that, finally, the phenomena accompanying an increase by cambium, 

 such as dilatation, formation of periderm, &c., also in themselves resemble those of 

 normal examples. Hence also the same terms will be used, and in the same sense 

 as in the foregoing paragraphs, except when special modifications are described by 

 special terms. 



The relations now under consideration differ from one another and from normal 

 cases, both qualitatively and quantitatively, to a very variable degree, and are con-- 

 nected one with another, and with normal cases by various intermediate forms. If 

 the latter be neglected, we have to deal with the following main phenomena. 



1. Anomalous distribution of the tissues in zones of wood and bast, with 

 normally derived, normally arranged, and perrnanently active normal cambium: 

 Sects. 182-186. 

 . 2, Abnormal formation and arrangement of cambium, wood, and bast: — 



(a) Besides the normal cambial ring a second appears, concentric with the 

 first, at the inner limit of the ring of wood ; Sect. 187. 



{i) In place of the one normal cambial ring in the ring of bundles, there 

 appear round the primary vascular bundles several separate cambiums side by side, 

 either one round each vascular bundle, or one round each group of vascular bundles. 

 Their position between the xylem and phloem of the bundle or bundles, and the 

 arrangement of the secondary products of wood and bast relatively to the latter, 

 resembles that in normal cases, Sects. 188, 189: rarely it is inverted, Sect 190. 

 Their productiveness is (compared with c) permanent. To distinguish them from 

 the normal general cambiums they may be called partial, and the rings or zones of 

 secondary growth derived from them partial thickening-, wood-, ov bast-rings in contrast 

 to the normal general ring. For shortness' sake, the woody ring is often simply 

 spoken of when the whole ring is meant. 



(f ) Renewed thickening zones. The increase in thickness begins normally, then 

 stops, and is continued by a new cambial zone, which is formed from secondary 

 meristem in the parenchyma outside the first, and this, as well as an unlimited 

 number of successive ones, may behave like the first, and like it be replaced by 

 a fresh one. The successive zones, or cambial layers are nearly concentric, and 

 arise in centrifugal order ; their arrangement and productiveness are normal, as long 

 as they continue : Sect. 191. 



(d) Extra/ascicular cambium. The cambial zone does not, as in normal cases, 

 pass through the primary bundle-ring, but lies entirely outside it ; the arrangement of 

 the products of its activity differs from the normal: Sects. 192 and 196. 



3. Abnormal dilatation of the internal old parenchyma belonging to the xylem, 



