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and Histogeny of Strychnos. 
Structure of the Root. 
We are not acquainted with any previous observations on 
the root of this genus. We were not able to obtain material 
sufficiently advanced to decide the most interesting question, 
namely that as to the existence of phloem-islands in the root. 
The oldest roots at our disposal had a xylem ring about 
eighteen cells in radial thickness, whereas in the stem the 
formation of phloem-islands does not begin until about double 
this amount has been formed. Hence no negative conclusion 
can be drawn. We were able, however, to prove the existence 
of medullary phloem in the root of .S', spinosa (the only species 
examined), and as this appears to be an uncommon structure 
among Dicotyledons, it will be desirable to give some account 
of the anatomy of the roots of this plant. 
The roots examined were from two sources, the Royal 
Gardens at Kew, and the garden of the Society of Apothecaries 
at Chelsea. The former plant is certainly S', spinosa , and the 
latter in all probability belongs to the same species. The 
differences in structure between the roots of the two specimens 
may well be due simply to differences of age. The largest 
roots examined were about 4 mm. in diameter. They are of 
polyarch structure, ten being a common number for the xylem 
or phloem-groups. The cortex is wide, and persists for a long 
time. The hypodermal layer is cuticularized, and forms a 
well-marked exodermis. The subjacent cells often divide 
to form an external periderm. This is, however, only a 
temporary structure, for the pericycle ultimately gives rise 
to an internal periderm of great regularity. In the main 
roots the pith is relatively very large, the xylem for a long 
time forming only a relatively narrow ring. The formation of 
secondary phloem is most active opposite the primary phloem- 
groups, so that the latter become pushed out into the pericycle, 
causing local compression of tissue. The appearance of these 
prominent masses of phloem is quite like that of the phloem- 
islands of the stem at an early stage of development, but we 
have no evidence to show that the phloem-groups of the root 
ever become enclosed in the wood. 
X 
