PRATT: CYCLOLOMA ATRIPLICIFOLIUM. 97 



has just arisen. A similar arc, forming the fourth ring of xylem 

 in region IV, is shown in fig. 52, n. The arcs, in a ring of secondary- 

 arcs of one region of stem, anastomose both tangentially and 

 radially with the arcs, in the corresponding ring of secondary 

 arcs, in the region of stem below (figs. 5, n, and 29, n). 



The number of xylem-phloem zones on the various sides of the 

 stem may differ, ranging from two to four in region IV (fig. 5); 

 from five to eight in region V (fig. 6) ; and from eight to twelve in 

 the part of the main axis having the greatest diameter. 



The xylem groups of the primary vascular bundles are not in- 

 cluded in the woody cylinder in region IV; for only the outer part 

 of the primary pericycle, on various sides of this region of stem, 

 lignifies completely enough to be included as a part of the woody 

 cylinder (figs. 5, e", and 11, e"), and the rest of the woody cylinder 

 in region IV is anomalous tissue, composed of the xylem zones 

 holding imbedded the phloem zones, as shown in figs. 5, and 29, r". 

 On other sides of the stem, in region IV, all the cells of the primary 

 pericycle (fig. 5, e\ e", and/) and primary medullary rays (fig. 5, g) 

 have cellulose walls, and are not included in the woody cylinder. 

 In all regions of stem below region IV, none of the cell walls of 

 the primary pericycle (fig. 25, e', e" and f) and primary medullary 

 rays (fig. 44, g) have lignified deeply enough to be included in the 

 woody cylinder, and the woody cylinder in these regions of stem 

 has been formed by anomalous growth only. (See figs. 6, and 

 29, s".) 



The relative radial breadth of the xylem-phloem zones is shown 

 in cross section in figs. 5 and 6. The anomalous zones are com- 

 plete rings around the stem, or as segments of rings have an irregu- 

 larly concentric arrangement in cross section, and undulate slightly 

 in a radial direction in their course around the stem (figs. 5 and 6) . 

 The xylem zones and the phloem zones anastomose both tangen- 

 tially and radially (figs. 5, u; 6, u; and 29, u). 



The xylem zones are generally made up of the tracheae, a few 

 lignified parenchyma cells bordering the tracheae, and the numer- 

 ous wood fibers (fig. 51, p). The wood fibers are shown in longi- 

 tudinal view in fig. 24. In some sections of region V and below, 

 the tissue lying on the inner side of some of the xylem zones is 

 made up entirely of wood fibers (fig. 53, p") ; and the remainder 

 of the xylem in each of these xylem zones (about 80 per cent of 

 the entire zone) is composed of wood parenchyma and tracheae 

 (fig. 52, q"). 



7— Sci Bui X. 



