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 cellular deposit between the former and the wood is analogous 
to cambium in an organised state, belonging equally to the 
wood and the bark. Wliat is so exceedingly remarkable 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 
Bauhinia from Colombia {fig- 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 stratum of woody tissue, enclosing, at irregular 
distances from the centre, very unequal 35 
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 concavities turned towards 
the pith. 
In the stem of a Passion-flower in my 
possession from Colombia {fig- 36.), 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 di- 
visions of the vascular system are 
separated. This vacancy is nearly 
filled with bark, which projects 
into the cavity. 
