354 YOUNGKEN— ON THE MYRICACEAE 



3. Secondary cortex whose cells are tangentially elongated and small- 

 est in the outermost portion, becoming larger as one passes toward the 

 phloem. Usually three or four of the outer layers of the exocortex 

 region are devoid of intercellular air spaces. The remaining layers 

 show numerous air spaces which are for the greater part small and 

 angular. Most of the cortical parenchyme cells contain spheroidal 

 starch grains with a central cleft hilum, either simple or 3-compound. 

 Some, however, contain rosette aggregates and monoclinic prisms of 

 calcium oxalate while others have their walls thickened and are filled 

 with a yellowish-brown substance which presents the following reactions: 

 It is insoluble in cold or boiling water, cold concentrated potash solution, 

 ammonia, alcohol or xylol. It is soluble in boiling nitric acid, boiling 

 concentrated potash solution and hot solution of sodium hypochlorite. 

 This substance has been termed " lignine-gommeuse " by Tison (8) and 

 Chevalier, (7 p. 133). 



Sclerenchyme fibres which are quite narrow are few and usually 

 isolated singly or in small groups of 2, 3 or rarely 4 amongst the cells 

 of the cortex. 



4. Endodermis whose cells do not differ materially from those of 

 the adjacent cortex. 



5. Fibro-vascular bundles of the open-collateral type, consisting of 

 phloem, cambium and xylem regions separated by medullary-rays. 

 The phloem region is comparatively wide. Many of the medullary-rays 

 in this region are broadened out in fan-shaped fashion. The bast fibres 

 are arranged singly or in groups forming interrupted circles. They are 

 more numerous in the metaphloem than in the protophloem region. 

 Crystal-fibres containing monoclinic prisms of calcium oxalate accom- 

 pany the bast fibres. Starch grains and tannin are found both in the 

 phloem cells and the phloem medullary rays. Many of the phloem cells 

 and air spaces contain monoclinic prisms of calcium oxalate. Fre- 

 quently several crystals are present in one cell or space. 



The xylem is porous and traversed by numerous medullary-rays, 

 continuous with those of the phloem. The medullary-ray cells of this re- 

 gion are more radially elongated and thickened than those of the phloem, 

 but resemble the latter in their content. 



The tracheae are more or less polygonal in transverse sections and 

 show barred septa. Some of them contain Actinomyces which has 

 found its way into them from the tubercles. This organism is always 

 associated with debris, presumably due to its eroding action upon the 

 tracheal walls. Tyloses are frequent. The walls of the tracheae are 



