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1920] 



LANGDON—DIOON SPINULOSUM 



125 



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

 leaf gap or foliar ray; />, 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 ; 

 x, primary wood ; ph, 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: 5/, 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 7 6 1 , c, c l , etc., 

 traces of scale leaf; cs, cotyledonary strands; i?, vascular system of root; X4. 



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

 traces, a 7 a 1 , b, b 1 , c, c x } 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; 5, B> two of the four principal groups of stem bundles; lg, leaf gaps 

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



Fig. 9a. — Three-year-old seedling; X0.5. 



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 u L 2 , L 3y first, second, and third 

 leaves of crown; second leaf not shown and only part of third leaf; l f x , /j 4 , 

 horizontal strands entering adaxial part of leaf one; h 2 , /i 3 , ventral strands 

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



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

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

 X2.5. 





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