57° 



SECONDARY CHANGES. 



the root of Polygala Senega ' belongs to this series : here, as a rule, the wood grows 

 strongly in thickness only in one approximate longitudinal half, the bast in the other. 

 The former, as seen in transverse section, attains the form of a half-circle with the 

 periphery turned towards its stronger growing side, or of a circle with a broad piece 

 cut out of' it on the weaker side. The transverse section of the bast appears as 

 a narrow segment of a ring surrounding the more strongly grown half of the wood, 

 on the other side as a large segment of an ellipse. In the dried root the stronger band 

 of bast projects as the well-known keel. 



Sect. 183. The inequalities in question appear in much more characteristic form 

 in the stems of lianes with deeply grooved wood, and with bast^plates which project 

 into the grooves : Bignoniacese, Phytocrene, and others to be named below. 



In the climbing ^2^w«za«« ^, Figs. 224—226, the secondary growth of wood 

 and bast is derived from a normal ring of cambium, and begins with the formation 

 of a zone of wood and bast, of normal structure and equal thickness all round, 



^iS- ==4- Fi& =23. Fig. 226. 



FIG. 224-— Anisostichus capreolata Eur. Transverse section through a four years' old branch, X 3. The annual rings 

 and medullary rays are represented in the wood by radial bands, the bast-layer and bast-plates by concentric lines. The 

 elongated figures in the peripheral cortex and the dark lines in tlie latter and in the four plates represent the fibrous 

 bundles ; ^the four larger ones. The pith is dotted. 



Fig. 22s.— Transverse section through a non-identilied Bignoniaceous stem (Pleonotoma!), from Schleiden, Gmndz.; nat. 

 size. 



FIG. 226.-Melloa populifolia Bur. (Bignonia No. 17, Fr. Muller. Botan. Zeitg. 1866). Transverse section through a 

 branch, X 2. Bast and bast-plates shaded, wood left white. The four first bands of wood, which have remained behind, 

 marked thus (•) i medullary sheath shaded radially, pith white. The dotted parts round the medullary sheath are large 

 islands of parenchyma, the subsequent dilatation of which splits up and bursts the wood. 



i. e, like a ring. The latter is limited from the primary outer cortex by an inter- 

 rupted zone of fibrous bundles. In each internode there are four bundles of this 

 zone (/), which are from the first larger than the rest. They' lie always, according 

 to Crijger, in four planes, which alternate regularly with the orthostichies of leaves, 

 and are perpendicular with reference to the straight internode : in transverse section 

 they are arranged crosswise. 



At the beginning of the secondary growth in thickness, the increase of the wood 

 in the longitudinal bands opposite the four large crosswise fibrous bundles is left 



' Walpers, Botan. Zeitg. 1851, p. 297; Wigand, in Flora, /. c; Figures in Wigand, Phaima- 

 cognosie, and Berg. Botan. Zeitg. 1857, Taf. I; Atlas, Taf. VIII. 



>■ Gaudichaud, Recherches, &c., sur I'organographie, &c., des veg^taux (M^m. presentees i 

 1 Acad, des Sciences, torn. VIII), Paris, 1841 ; Idem in Archives de Botanique, II. (i833).-A. de 

 Jussieu, Monogr. des Malpighiac^es ; Archives du Museum, torn. III. (i843)..-Mettenius in Lin- 

 nsea Bd. 19 (i847).-.Schleiden, Giundzuge, 3 Aufl. II. i6s.-Cruger. Botan. Zeitg. 1850, p. loi.- 

 V. Mohl Botan. Zeitg. 1855, p. 875.-Bureau, Monogr. des Bignoni.-vc^es, Paris, 1864, p. 120 : Id. in 

 Bullet. Soc Bot. de France, 1872, p. i4._F. MiiUer, Botan. Zeitg. 1866, p. 65. [Westermaier n. 

 Ambronn, Lebenswgise u, .Stiuktur d. Schling-u. Kletterpflanzen. Flora, 1881 ] 



