212 MALPIGHIADS BIGNONIA. [BOOK i. 



the outer layers are, it is to be presumed, liber and epidermis ; 

 and the cellular deposit between the former and the wood is 

 analogous to cambium in an organised state belonging equally 

 to the wood and the bark. What is so exceedingly remark- 

 able is the complete intermixture of the vascular and cellular 

 systems, so that limits no longer exist between the two. 



I have a specimen of the twisted compressed stem of a 

 Malpighiad from Columbia (fig. 37.), in which there are no 

 concentric circles, properly so called ; but in which there are 



fig. 37. 



certain irregular wavy zones, consisting of a layer of cellular 

 tissue coated by a stratum of woody tissue, enclosing, at irre- 

 gular distances from the centre, very unequal portions of the 

 vascular system. The pith is exceedingly excentrical ; and the 

 medullary rays, which are imperfectly formed, do not all 

 radiate from the pith, but on the thickest side form curves 

 passing from one side of the stem to the other, their con- 

 cavities turned towards the pith. 



In the stem of a Bignonia in my possession, from Colombia 

 (fig. 38.), the vascular system is divided into four nearly 

 equal parts, by four short thick plates radiating from the 

 pith, and consisting of woody tissue, with a very few vessels. 

 These plates are not more than one-third the depth of the 

 wood; so that between their back and the bark there is a 

 considerable vacancy, by which the four divisions of the 



