DEVELOPMENTAL CHANGES IN THE VASCULAR CAMBIUM IN LEITNERIA FLORIDANA

Developmental changes in the vascular cambium of Leitneria floridana , a shrub, were determined primarily by an analysis of the secondary xylem. During the production of the first growth ring of secondary xylem, 37% of the anticlinal divisions in the fusiform initials were lateral, the remaining were oblique. The oblique partition averaged ½ of the length of the dividing initials during this period of growth. Following their origin in anticlinal division, daughter cells elongated at a rapid rate until they were about as long as the mean for all cells, and then most cells elongated at a slow rate. Almost all initials survived during the formation of the inner secondary xylem (growth rings 1–10), and few new rays were formed from fusiform initials. During the production of the outer secondary xylem (growth rings 22–26), lateral divisions accounted for less than 5% of all anticlinal divisions. The oblique partition averaged only ¼ of the length of the dividing cells during this period, although the mean length of dividing initials was relatively constant throughout secondary growth. About 20% of the initials studied during the deposition of the outer secondary xylem disappeared from the cambium, and many others were transformed into ray initials. The findings are discussed in relation to the developmental changes in the vascular cambium in plants of different habits.