LTANE-STEMS 



r.ni 



simple condition prevails, for example, among Bignoniaceous tendril- 

 climbers, and also in various Malpighiaceae {Tetrapteris, Banisteria, 

 Stigmaphyllon) and APOCYNACEAE, in the genus Ph//focrenc, etc. 

 Among the Bignoniaceae, the output of secondary wood is relatively 

 small from the first at four points, which are arranged in the form of a 

 cross, while the production of secondary phloem at these points is 

 correspondingly increased. As a result, the woody cylinder appears to 

 be provided with four longitudinal grooves. These grooves become 

 constantly deeper, as growth in thickness proceeds ; but since they are 

 filled with secondary phloem, the cross-sectional outline of the whole 

 vascular cylinder is not appreciably affected by this unequal develop- 

 ment of the secondary xylem. The cambium itself becomes broken up, 



Fig. 2S4. 



T.S. through a four-year- 

 old twig of Bignonia capreo- 

 lata. The woody cylinder is 

 traversed by four furrows or 

 grooves occupied by phloem. 

 X3. After De Barv. 



Pig. -2S. r ,. 



T.S. through an undetermined 

 Bignoniaceous stem (? Pleonotoma 

 sp.). Nat. size. After Schleiden. 



Fig. 2S6. 



T.S. through a twig of Melloa populi- 

 folia. The lobed woody cylinder is 

 shown in white, the phloem shaded. 

 X2. After De Bary. 



as a result of its peculiar behaviour, into a succession of strips, the four 

 widest among which lie opposite the four projecting ridges of wood, 

 while the narrower portions are situated at the bases of the grooves. 

 In certain Bignoniaceae the furrows always remain four in number 

 (Fig. 1384); in other species, on the other hand, additional grooves are 

 continually interpolated, as the result of a reduction of wood-production 

 at an increasing number of points in the circumference of the cambium. 

 The embedded plates of secondary phloem also often increase in width 

 towards their outer ends by a series of step-shaped increments 

 (Fig. 286). In this way the whole woody cylinder becomes split up 

 into a large number of separate lobes and strips. 



In certain Malpighiaceae, Bignoniaceae, etc., the splitting up of 

 the wood is carried a stage further, owing to secondary changes in 

 the xylem-parenchyma and pith. The primarily continuous, though 

 greatly lobed, woody cylinder becomes completely broken up, owing 

 to the active intercalary growth of interpolated masses of par- 

 enchyma. According to Schenck, this " dilatation-parenchyma " in 



