Arber . — On the Roots of Medullosa anglica. 433 
EXPLANATION OF PLATE XX. 
Illustrating Mr. Arber’s paper on Medullosa anglica . 
All the sections (AM i-A M 29) are in the Woodwardian (Sedgwick) Museum, 
Cambridge. All the figures, except Figs. 4 and 5, are microphotographs from the 
actual sections by Mr. W. Tams, Cambridge. Some of these should be examined 
by means of a hand lens. Figs. 4 and 5 are photographs by Mr. Tams, from 
drawings by Mr. E. Wilson, Cambridge. 
Fig. 1. Complete transverse section of a root, p.d., periderm; p.x., proto- 
xylem ; x 2 ., secondary xylem ; r.x., xylem of rootlet ; z., zone of thin-walled 
tissue, comprising phelloderm, pericycle, and phloem ; gr., groove in the periderm, 
x n§. Section AM 18. 
Fig. 2. Part of a transverse section of a root, internal to the periderm, and 
opposite a protoxylem-group. p.d., periderm; phg ., phellogen ; ph.d., phello- 
derm; p.c., pericycle; m.r., main medullary ray ; p.x. , protoxylem ; r.x., xylem of 
rootlet, x 75. Section A M 24. 
Fig. 3. Part of a transverse section of a root, internal to the periderm, and 
opposite one of the convexities of the secondary xylem. p.d., periderm ; p.c., 
pericycle ; b.z., phloem-zone ; ft 1 ., secondary phloem ; s.t., sieve-tubes ; bp., bast 
parenchyma ; b 1 ., primary phloem, x 75. Section AM 15. 
Fig. 4. Drawing of sieve-tubes as seen in a longitudinal section of the stem 
of Medullosa anglica. s.p., sieve-plates, x 280 approximately. Section A M 9. 
Fig. 5. Drawing of a sieve-tube as seen in a longitudinal section of a root 
of Medullosa anglica. s.p., sieve-plates, x 430 approximately. Section AM 28. 
Fig. 6. Complete transverse section of a root, r.l., lateral root ; gr., groove in 
periderm, x uf. Section AM 23. 
