MEDULLARY RAYS. 229 
have no distinctly marked medullary rays, either in the wood 
or in the bark (Radix Ipecacuanhe and in Rad. Tarazaci). 
The medullary rays of rhubard (Fig. 146 6), which only oc- 
cur regularly in the cortical portion, are very characteristic 
with regard to their course and contents. Within they are 
variously serpentine, and ‘therefore, since they consist of cells 
with reddish-yellow contents, produce the peculiar spots on the 
surface of the peeled rhizome and the marbled appearance of 
the interior.* 
In those fibro-vascular bundles where, by the formation of 
the bundies themselves, the activity of the cambium is termi- 
nated already at the growing point, no medullary rays are 
ele sea 
ty 
Fig. 146 b.—Transverse section of Rhubarb. e, remnants of the bark, which has 
been pared off: c, cambium, a, medullary rays of the marginal portion; s, stellate 
spots; m, fundamental tissue. 
formed; hence they are wanting in the monocotyledons and in 
the vascular cryptogams. 
Although, for example, the vascular bundles in a number of 
monocotyledonous roots are closely connected with each other, 
and are arranged in the form of compact, closed rings (Rhiz. 
Graminis, Rhiz. Caricis, Rad. Sarsaparille, and rootlets of 
Veratrum), the medullary rays are nevertheless wanting in these 
rings. 
The cells of the medullary rays have the function of con- 
luctiag in a radial direction. But they are also receptacles for 
1 Berg's “ Atlas,” Plate xii. 
