PRATT: CYCLOLOMA ATRIPLICIFOLIUM. 95 



THE WOODY CYLINDER. 



In region II there is a beginning of the formation of a woody 

 cylinder, consisting of xylem groups of primary vascular bundles 

 (fig. 3, j), and lignified pericycle (fig. 3, e" and /) and primary 

 medullary rays (fig. 3, g), and holding imbedded the strands of 

 phloem belonging to the vascular bundles (fig. 3, j). The woody 

 cylinder of region II is mapped out in fig. 3, and the detail of the 

 tissue pf the woody cylinder in a portion of a cross section of 

 region II is shown in fig. 8. The woody cylinder in region III, 

 mapped out in fig. 4, is larger than in region II, due to the larger 

 size of the cells of the areas, e" and /, of the primary pericycle 

 (fig. 9) and primary medullary rays (fig. 9, g) included, and to the 

 addition of anomalous xylem (fig. 4, m), formed by anomalous 

 grov\i:h. 



The anomalous growth consists in the formation of one or sev- 

 eral broad zones of xylem around the stem, and a narrow, broken 

 zone of tissue (made up of phloem groups, secondary medullary 

 rays, and from one to several rows of pericycle cells exterior to 

 the phloem groups and secondary medullary rays), having thin 

 cell walls and located just exterior to each xylem zone, both kinds 

 of zones being formed by broken rings of arcs of secondary meri- 

 stem, which arises successively around the stem in the pericycle. 

 The arcs in each successive ring of arcs of secondary meristem 

 are active for a time, but cease their activity before the next 

 younger ring of arcs arises. 



For convenience in presentation of the anomalous structure, 

 frequently in this article the broad xylem zones are designated as 

 xylem zones, and the narrow, broken zones having thin cell walls, 

 as phloem zones. 



The number of cells in the outer area of pericycle is consider- 

 ably greater in region III (figs. 4, e', and 9, e') than in region II 

 (figs. 3 and 8) . On various sides of the stem, arcs of the inner rows 

 of the cells in this area of pericycle have just produced a secondary 

 meristem in region III (fig. 47, n), and other secondary arcs, 

 having arisen earlier on other sides of the stem, are in different 

 stages of progi-ess (figs. 48, n, and 49, n). Anomalous xylem has 

 been formed on some sides of the stem in region III by the sec- 

 ondary arcs of meristem, as shown in figs. 4, m, and 29, p", and 

 48, m. On some sides of the stem the secondary arcs have not 

 yet arisen, as shown in fig. 9, e'. 



In regions of stem just below region III, the arcs latest to be 

 differentiated in the first ring of secondary arcs have arisen; and 



