DIV. I 



MORPHOLOGY 



183 



produced from the cambium ring in the usual manner, and an inner, normal wood 

 cylinder of AXIAL wood is formed. Such normally-formed axial wood cylinders 

 are common to many otherwise abnormally developed lianes. The cambium ring 

 of the Bignoniaceae, after performing for a time its normal functions, begins, at 

 certain points, to give off internally only a very small quantity of wood, and 

 externally a correspondingly large amount of bast. As a result of this, deep 

 wedges of irregularly - widening bast project into the outer so-called PERIAXIAL 

 WOOD (Fig. 212). The originally complete cambium becomes thereby broken into 

 longitudinal bands, which are broader in front of the projecting wood than at the 

 apices of the bast wedges. As the periaxial wood is always developed from the 



FIG. 211. Transverse section of 

 the stem of Serjania Laruot- 

 teuna. sk, Part of the rup- 

 tured sclerenchymatous ring 

 of the pericycle ; I and I*, bast 

 zones ; Ig, wood ; in, medulla, 

 (x 2. After STRASBURGER.) 



FIG. 212. Transverse section of the stem of one of the 

 Bignoniaceae. (Nat. size. After SCHENCK.) 



inside and the wedges of bast from the outside of their respective cambium bands, 

 they extend past each other without forming any lateral connection. Several 

 woody cylinders are found in a number of tropical lianes belonging to Serjania 

 and Paullinia, which are genera of the Sapindaceae. This anomalous condition 

 arises from the unusual position of the primary vascular bundles, which are not 

 arranged in a circle but form a deeply -lobed ring ; so that, by the development 

 of interfascicular cambium, the cambium of each lobe is united into a separate 

 cambium ring. Each of these rings, independently of the others, then gives 

 rise to wood and bast (Fig. 211). 



2. Epiphytes ( 90 ). In another group of cormophytes the leaves 

 obtain stronger light by the plants being able to establish themselves 

 on the stems and branches of high trees instead of being rooted in the 

 ground. Such plants are termed epiphytes. Since the trees only 

 afford them support they may be replaced by inorganic substrata such 

 as rocks. The supply of the requisite water and nutrient salts will 

 evidently be a difficulty. Consequently special adaptations are found 

 to meet this ; in many epiphytes shoot-tubers serve for water storage 



