412 DR. ERIC DRABBLE ON THE 
sclerenchymatous zone shows wedge-formation and xylem V's occur. More proximally 
a complete gap in the sclerenchyma is found, and the endodermis dips in and becomes 
diseontinuous. In addition to this several depressions occur in the cylinder, into which 
the endodermis sinks, but is quite continuous. At such a depression the arrangement of 
bundles is rather peculiar, the insinking of a phloem-group and convergence of two 
protoxylem-groups by their external ends being very well marked. (fig. 11.) 
In the pith of such a root several free sclerenchymatous strands occur, each with one 
to three central vessels. 
(39) DypsIs MADAGASCARENSIS, Hort. 
The outer walls of the limiting-layer cells are often much thickened, all the other walls 
remaining of the usual thin type. Following this is a zone of small elements filled with 
dark brown contents. Internally this zone gives way to the inner parenchymatous cortex, 
through which run bundles of fibres. The internal layers are provided with many-ranked 
small air-spaces. The endodermis is lignified and much thickened in the usual manner. 
The pericycle consists of one or two layers of cells. The xylem and phloem are embedded 
in a more or less lignified fibrous zone. V’s are of frequent occurrence in the xylem, the 
elements of which are confined to the periphery of the cylinder. In the centre is alarge 
parenchymatous pith with very irregular air-spaces. One sclerenchymatous strand 
enclosing a single vessel runs laterally in the pith. 
In larger roots the histological structure is similar, but the sclerenchymatous zone, 
instead of forming a complete circle, is composed of two entirely separate lobes, the free 
ends of which are inflected. Into the space between the two lobes the endodermis of each 
lobe dips and is lost in the general ground-tissue of the root. In these gaps are found 
bundles of fibres exactly like those of the cortex ; these may penetrate the internal ground- 
tissue of the cylinder fora short distance. In the medulla are free sclerenchymatous 
strands with central vessels. One of these occurs just opposite one of the gaps in the 
cylinder, and externally to the central vessel in this strand runs a phloem-group. 
(Text-fig. 12.) 
Fig. 12. 
ME still older portions the cylinder is split up into many separate arcs, the larger ones 
containing as many as forty xylem-groups. The ends of the are are inflected as in the 
section Just described. The smaller arcs may contain only one xylem-group, flanked 
