58 INTRODUCTION TO CEYPTOGAMIC BOTANY. 



the central cord, which consists of a hard cartilaginous mass of 

 closely anastomosing threads as in the external coat, is divided 

 into wedges so as to form a further analogue of an Exogenous 

 stem. In process of growth those plates divide, and resemble 

 some of the more anomalous arrangements of the wood in 

 Exogens. 



44. The differences of habit, and even of structure, in closely 

 allied flowering plants, are equally deceptive. Take, for in- 

 stance, the chmbing and the erect Bauhinias. The flattening 

 or angularity of the stem, in this and in many other genera 

 of the same natural order, as also amongst Sapindacece, Bigno- 

 niacecB, Malpighiacew, &c., the compression and torsion to 

 which they are subject, and, in fact, the necessities of the 

 plants, induce anomalies in the direction of the medullary 

 rays, the development of parenchyme, the intrusion of cortical 

 matter, &c., which almost defy investigation.* In some species 

 as Cassia quiiiquangulata, Rich., which is not always a 

 climber, there is at different epochs, and under different circum- 

 stances, a very different structure,! insomuch that Criiger 

 says expressly, that if, on the one side, perplexity arises 

 from the complication of the wood, on the other hand the 

 differences in individual plants show that a great part of these 

 anomalies may depend on accidental causes, as soil, position, &c. 

 If the office of the ducts be really to carry air to every part of 

 the plant, it is clear that the size of these ducts must be 

 increased in proportion as the stems are subjected to distortion 

 and compression. 



45. Take, again, the difference of structure in different 

 species of Myzoclendron. In M. brachystachyum, the wood 

 is deposited in two series of wedges, not always very regular, 

 and at first sight calhng to mind, as regards their disposition, 

 some of the climbers mentioned above. In M. quadriflorum, 

 the inner series is represented by a single obUque wedge in the 

 axis, while in M. linearifoUum, there is but a single series. 

 When the disposition of the various tissues of which these are 



* See Criiger in Bot. Zeitimg, 1850, 1851 ; Mettenius in Liuniea, vol. 

 xix.; the Memoirs of Juasieu, Schleiden, &c. 

 t Criiger, Bot. Zeit. 1801, p 469. 



