78 



ORGANOGRAPHY. 



BOOK I. 



woody tissue, containing some very minute spiral vessels ; and, 

 finally, the whole is enclosed in a cellular integument, also con- 

 taining spiral vessels of small size. In this singular plant the 

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

 the cell alar 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 remarkable is the 

 complete mtermixture 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 

 Bauhinia from Colombia {Jig. 35.), in which there are no con- 

 centric circles, properly so called ; but in which there are cer- 

 tain irregular flexuous zones, consisting of a layer of cellular 

 tissue coated by a sti'atum of woody tissue, enclosing, at irregular 

 distances from the centre, very unequal 

 portions of the vasculair 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 concavities turned towards 

 the pith. 



In the stem of a Passion-flower in my 

 possession from Colombia {Jif/. 36.), the 

 vascular system is divided into four 



36 



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 di- 

 visions of the vascular system are 

 separated. This vacancy is nearly 

 filled with bark, which projects 

 into the cavity. 



