ANOMALOUS THICKENING IN DICOTVLEDONS AND GFMNOSPERMS. 577 



The above description is derived partly from Mettenius' account, partly from 

 the same transverse sections of the stem as the latter was based upon. Some other 

 transverse sections, and the figure in Lindley /. c, show a structure which differs in 

 many details from that described. But whether we have to deal with individual or 

 specific differences is uncertain, since there were no definitions of the species in the 

 material used. According to Jussieu^ there is also in Phytocrene a formation of 

 dichotomous lobes of the protrusions of the wood. 



Sect. 185. Similar phenomena to those in Bignonias and Phytocrene, with 

 similar differences to those between these plants, are found developed to a different 

 extent in the climbing shrubs of different other families: within the cylindrical or 

 slightly ridged stem are fiat, or very deep infoldings of the xylem, and bast-plates of 

 corresponding form, which fit into these. Disregarding certain of the cases in question 

 which are not defined with certainty, and are not very typical, we may here name 

 members of the Malpighiaceee, from the genera Tetrapterys, Banisteria, also Stig- 

 maphyllon ^, and Peixotoa sp. ^ Apocynese of the genera Condylocarpon *, Echites ; 

 the Asclepiad Gymnema silvestre, a species of Celastrus^ and a Tournefortia ^ 



The Peixotoa (/. c. Fig. 2) shows eight blunt low protrusions of the xylem, within 

 the cylindrical outer cortex, which is surounded by great rent masses of cork or bark. 

 Miiller's Tetrapterys (/. c. Fig. i) shows very similar phenomena to those in the Bignonias 

 above noticed, p. 574 under II. In the younger round stems or branches, up to i<=™ in 

 thickness, the xylem has six sharp incisions, filled by bast-plates ; in stronger stems there 

 appears in addition to these, and accompanying their radial development, a further single 

 or double splitting of the protrusions of xylem by intruding bast-plates, that is a 

 formation of dichotomous lobes of the transverse sections of the xylem. The older parts 

 of the bast-plates are constricted and pressed together by tangential extension of the 

 adjoining portions of xylem. It is uncertain whether the radial lateral faces of the 

 bast-plates remain surrounded by a layer of cambium. 



In Miiller's Condylocarpon {I.e. Fig. 4) the transverse section of the xylem of young 

 branches up to i*=™ in thickness is round, and equally thick on all sides. Then begins 

 the formation of incisions and of bast-plates fitting them — the number of those which 

 appear at first and simultaneously seems to be three ; in addition to the first, which 

 grow further in a radial direction, numerous fresh ones of similar character successively 

 arise, so that the whole system shows numerous irregular dichotomous lobes as seen in 

 transverse section. Here also there is found in older inner parts, for certain distances, 

 contraction and complete distortion of the bast-*plates by swollen protrusions, which 

 subsequently appear at the lateral faces of the protrusions of xylem ; here also it remains 

 to be investigated whether they arise from a cambial zone which is permanent from 

 the first at this point, or from one which appears subsequently. 



Sect. 186. An anomaly in the distribution of tissues, which goes a step further 

 than those hitherto spoken of, consists in the following peculiarity of certain woody 

 plants, viz. that they develope rings of wood, cambium, and bast in their normal 

 position, and without specially remarkable relations of form, but develope no si'eve- 

 tubes in the secondary bast, these being united with delicate parenchyma in bundles, 

 and enclosed in the xylem. 



'/.<". p. 122. ''■ A. de Jussieu, I.e. p. 106, 



= Fr. Miiller, I.e. * Idem. /.r, 



'^ Jussieu, I.e. p. 117. « Criiger, Botan. Zeitung, 1851, p. 468. 



pp 



