276 ON THE STRUCTURE OF THE BEET-ROOT. 
in the region where the external portion of the bundles is united 
with the woody portion. The fibro-vascular bundtes are smaller 
and smaller the more exterior they are; at the periphery they are 
scarcely more tha arely perceptible vascular point; they may 
even be destitute of vessels, and form their union only very re- 
in which one meets with neither fibrous bundles, nor distinct layers, 
nor medullary prolongations. In short, it contains none of the 
elements of a true A 
_ These details recall the arrangements which are met with in 
Dicotyledons which are termed heterogeneous (for example, some 
developed ; finally, on the exterior of the bundles there is merely a 
simple parenchymatous zone. 
f a vertical section is made through the young plant, the 
vascular bundles are seen to be separate beneath the cotyledons ; 
then they approach so insensibly that it is difficult to say where 
the medullary centre terminates ; a centimetre below the cotyledons 
the bundles are fused at the centre. A transverse section made at 
this point exhibits a central bundle incompletely divided into two 
parts; at the higher level the two bundles are distinct, and beneath 
the cotyledons there are four bundles, two being formed between the 
two primary ones for the formation of the cotyledonary expansions. 
The vascular bundles are surrounded by a white transparent zone; 
externally is a parenchyma composed of two zones : the inner is dense, 
succulent, red, pink, or white, according to the varieties ; it has its 
