ANATOMY OF THE ROOTS OF PALMS. 471 
gap, a line of cells of endodermic nature extends inwards into the cylinder. (Text- 
fig. 18.) 
One greatly incurved are of the central cylinder was found to be completed in a 
curious fashion. A medullary strand possessing three symmetrical protoxylem-groups 
radiating from a central vessel, and alternating with the protoxylems, approaches distally 
to the interior of the incurved arc and closes the gap by fusion of the fibrous tissues, 
thus enclosing a central parenchyma continuous above and below with the medullary 
ground-tissue. Of the three protoxylem-groups, two become arranged tangentially in a 
straight line, the third, pointing inwards, is considerably reduced. The endodermis is 
only incomplete at the most internal point of the cylinder thus formed. 
Another interesting condition was observed where a complete cylindrical portion of 
the central cylinder is approached distally from the interior by a medullary strand, with 
four xylem- and four phloem-groups, which eventualiy fuses with it, thus causing a very 
irregular arrangement of xylem and phloem on the interior of the composite eylinder so 
formed. On following this cylinder distally, the ordinary symmetrical alternation of 
xylem and phloem is gradually attained, and thus a cylinder is produced with four more 
xylem-groups than the original one. 
Lower down in the root this opens internally and its central parenchyma becomes 
continuous with the medullary parenchyma, and finally, traced to the apex, the group is 
represented as a distinct, curved, procambial strand, consisting of xylem- and phloem- 
groups embedded in fibrous ground-tissue. 
The internal fibrous strands which contain xylem and phloem tend to fuse with the 
peripheral system of the cylinder. In those strands possessing only a single central 
vessel no such tendency manifests itself, these being continued as separate procambial 
strands into the apex. , 
On following the separate arcs of the cylinder towards the apex, they are seen to open 
out internally and finally to unite, gradually losing the lobed outline, and eventually 
forming a complete uninterrupted meristematic cylinder. Sometimes where fusion of 
the arcs takes place the endodermis is doubled. l 
Only in a long root can all these changes be observed ; in shorter roots the reduction 
to normal root-structure is incomplete. Only a very small proportion of the roots 
examined showed complete simplification. The union of the arc is always completed 
earlier (7. e. more proximally) on the abaxial than on the adaxial side, a single gap in 
the fibrous zone often persisting for a very considerable distance on the adaxial. side after 
the cylinder is otherwise complete and regular. Occasionally small groups lying well to 
the interior of the cylinder are externally provided with endodermis. 
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