U)OZ 



THIESSEN—DIOON EDULE 379 



Fig. 7a (2). —Stem tip from rapidly growing seedling, showing growing point 

 (st) in the middle and a leaf primordium (L) on each side; this section showed 

 numerous spindles in growing point and primordia. 



PLATE XXV 



Fig. 8. — Details of central region of embryo in median longitudinal section: 

 L, youngest leaf; st, stem tip; ep, epidermis; pt, pith terminating in stem tip; 

 pc, procambium; vp, vascular plate; ph, phloem; a, continuation of protoxylem 

 into the root; p, pith; pi, plerome; m, mucilage cells. 



Fig. 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 (/). 



Fig. ga. — 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 (ab, cd), xylem tissue, 

 ad, protoxylem; unshaded portion in aa' (cj), procambium; cj (gg / ), proto- 

 phloem; dotted line cj, boundary between procambium and protophloem. 



PLATE XXVI 



Figs. 10-15.— Series of cross-sections of cotyledonary traces: fig. 10, just 

 before joining vascular cylinder; fig. 15, after the several bundles have reunited 

 in upper extremity of cotyledon; px, protoxylem. X850. 



PLATE XXVII 



Figs. 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. X850. 



PLATE XXVIII 



Fig. 22.— Cross-section at low level of foliar trace of a three-year-old plant: 

 px, protoxylem (endarch); x, xylem, of which probably the larger portion is 

 centrifugal metaxylem and only a small portion is secondary xylem; ph, phloem; 

 pph, protophloem. X425. 



Fig. 23.— Section from the same strand as fig. 22, but considerably higher 

 up; px, protoxylem (mesarch). X425- 



Fig. 24.— Section of bundle from old leaf of quite a large plant just below 

 rachis: px, protoxylem (exarch); mx, metaxylem (centripetal); tc, thin-walled 

 cells; sx, secondary xylem; ph, phloem; pph, protophloem. X425- 



Fig. 25.— Cross -section of bundle in pinna: lettering as in fig. 24; note 

 absence of secondary xylem. X425. 



Fig. 26.— Median longitudinal section of very young leaf trace, showing 

 shape and arrangement of cells; shaded portion, earliest procambium. X1200. 



Fig. 27. — Cross-section of the same bundle as in fig. 26. 



PLATE XXIX 



Fig. 28.— Median longitudinal section of embryo at right angles to inner 

 faces of cotyledons. Xn. 



