125 LANGDON—DIOON SPINULOSUM [1020 



Fig. 5. — Mature wood: radial longitudinal section near lateral border of 

 leaf gap or foliar ray; p, pitted tracheids of secondary wood diverted to one 

 side into direction parallel to that of trace; sc, scalariform tracheids of trace 

 extending down between fibrous elements of main stele; X55. 



PLATE XVI 



Fig. 6. — Mature wood: tangential section of foliar ray; //, leaf trace, 

 scalariform tracheids of trace seen in both longitudinal and transverse section; 

 .v. primary wood; />//, disorganized phloem; mc, mucilage duct; X56. 



Fig. 7. — Adult wood: tangential view of foliar ray in vicinity of cambium, 

 tracheids constituting trace seen only in transverse section; X56. 



PLATE XVII 



Fig. 8. — Two-year-old seedling, diagram showing: si, origin and course 

 of vascular supply of one of first scale leaves; L, first year foliage leaf, and 

 I 2 second year foliage leaf, as traced from cleared material; a, a 1 , b, b 1 , c, c l , etc., 

 traces of scale leaf; cs, cotyledonary strands; R, vascular system of root ; X-+- 



Fig. 9. — Three-year-old seedling: diagram showing connection of lateral 

 traces, a, a 1 , b, b 1 , c, c 1 , d, d 1 , and e, with stem cylinder, and manner of anastomo- 

 sis to form horizontal girdles; A, D, two of the four main cotyledonary 

 bundles; S, B, two of the four principal groups of stem bundles; Ig, leaf gaps 

 corresponding to foliar gaps of adult stele illustrated in figs. 6, 7; X4.5. 



Fig . qa . — Three-year-old seedling ; X o . 5 . 



Fig. 10. — Median longitudinal section through apical portion of ten-year- 

 old plant, showing only one side of the three sets of horizontal girdles with 

 their associated lateral vertical strands; L I} L 2 , I 3 , first, second, and third 

 leaves of crown; second leaf not shown and only part of third leaf; l s s , l,\ 

 horizontal strands entering adaxial part of leaf one; h 2 , I?, ventral strands 

 apparently united with the two dorsal girdling strands Z, 1 and /i 4 ; X2.5. 



Fig. 11. — Diagram of entire vascular supply of first leaf, £,, fig. 10; com- 

 plete anastomosis of leaf traces to form one main horizontal girdling strand; 

 X2.5. 



