1908] THIESSEN—DIOON EDULE 379 
Fic. 7a (2).—Stem tip from rapidly growing seedling, showing growing point 
(st) in the middle and a leaf primordium (Z) on each side; this section showed 
humerous spindles in growing point and primordia. 
PLATE XXV 
Fic. 8.—Details of central region of embryo in median longitudinal section: 
L, youngest leaf; st, stem tip; ep, epidermis; pé, pith terminating in stem tip; 
be, procambium; vf, vascular plate; ph, phloem; a, continuation of protoxylem 
Into the root; #, pith; pl, plerome; m, mucilage cells. 
- Fic. 9.—Median longitudinal section of lower part of germinating embryo, 
showing lengthening of plerome, development of primary root, and fraying-off 
of epidermis and outer part of cortex (/). 
Fic. 9a4.—Diagram to show transition of protoxylem in the metaxylem, and 
transition of primary xylem from an inner to a central position in a young bundle: 
aa’, inner, and gg’, outer limits of bundle; shaded portion (a), cd), xylem tissue, 
ad, protoxylem; unshaded portion in aa’ (cf), procambium; cf (gg’), proto- 
Phloem; dotted line cj}, boundary between procambium and protophloem. 
PLATE XXVI 
Fics. 1o-15.—Series of cross-sections of cotyledonary traces: fig. 10, just 
before joining vascular cylinder; fig. 15, after the several bundles have reunited 
upper extremity of cotyledon; px, protoxylem. X850. 
PLATE XXVII - 
__ Mes. 16-21.—Series of cross-sections of leaf traces: fig. 16, just before 
joining vascular cylinder; figs. 17-20, at considerable intervals above each other; 
fig. 21, younger trace; shaded portion protophloem. X85. 
PLATE XXVIII 
Fic. 22.—Cross-section at low level of foliar trace of a three-year-old plant: 
pe, Protoxylem (endarch); x, xylem, of which probably the larger portion is 
centrifugal metaxylem and only a small portion is secondary xylem; ph, phloem; 
beh, protophloem. X 425. 
Fic. 23.—Section from the same strand as fig. 22, but considerably higher 
"WP; px, protoxylem (mesarch). x 425. 
Fic. 24.—Section of bundle from old leaf of quite a large plant just below 
— px, protoxylem (exarch); max, metaxylem (centripetal); %, atn-walled 
» S®, secondary xylem; ph, phloem; pph, protophloem. X425. 
1G. 25.—Cross-section of bundle in pinna: lettering as in fig. 24; note 
secondary xylem. X 425. ‘ 
'G. 26.—Median longitudinal section of very young leaf trace, showing 
and arrangement of cells; shaded portion, earliest procambium. %1200. 
Fig. 27.—Cross-section of the same bundle as in fig. 26. 
PLATE XXIX | 
—— 28.—Median longitudinal section of embryo at right angles to inner 
of cotyledons. X11. 
