278 ON THE STRUCTURE OF THE BEET-ROOT. 
proportion as they are older. Thus the vascular groups of the 
first circular formation, which originally were only rounded points, 
are greatly enlarged subsequently, and are bi-tri-furcate. e 
outer circles the vascular groups are in simple series less and less 
8 
similar to what has been described; the vascular formations are 
merely more numerous—on the fragment which we examined we 
counted ten vascular formations. Those which are the most external 
e the same characters as those which occupied the periphery 
The medulla which exists in the upper part of the hypocotyledonary 
stem is formed of cells at first transparent, then areolated, dilated, dis- 
posed without order, The woody bundles are formed of large vessels, 
flexuous, with spiral fibres more or les anastomosing, united b 
vascular or by fibrous tissue, white, sometimes a little orange (red 
var.), slightly transparent, composed of elongated cells, rounded or 
quadrangular, narrow, with rounded, slightly acute extremities, united 
end to end, or placed in the interval between two cells with very 
paren 
covered with ver finely granular matter. The medullary rays are 
formed of cells disposed in transverse rows ; they are cubical, some- 
times a little higher than wide, rarely a little elongated transversely ; 
their walls are opaque. The transparent parts, which represent the 
cortical bundles, and are placed externally and opposite the woody 
bundles, are formed of elongated cells like those of fibrous tissue ; but 
these cells enlarge towards the exterior, and become more dilated as 
they are nearer the medullary zone. Long tubes, attenuated at the 
extremities, are not met with in these transparent bundles as in some 
placed and with which they are blended. ‘The medullary zones 
which separate the circular formations which succeed are formed 0 
