ANATOMY OF TISSUES. 121 
of a central cylinder made up of a single radial bundle, or, as it 
may be considered, a collection of several. The radial bundle 
is common to all roots with very few exceptions, and it occurs 
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Cross-section through a young root after the bundles are started. Under the epidermis with 
the root hairs is the rind parenchyma, 7, which is bounded within by the endodermis, 
e, which later forms the cork layer. Inside the endodermis is the pericambium, pc’. 
The bundles are arranged so that the wood alternates with the bast. The cambium 
ring, c, which later develops the secondary growth, lies inside the bast at c and outside 
the wood at c’.— (Th. Hartig.) 
in only a very small number of stems. In it the xylem and 
phloem groups are radially arranged, that is, they lie next each 
other but on different radii. The simplest interpretation of this 
arrangement would be to consider the number of bundles equal 
to the number of xylem clusters, as for each of these there is a 
