Syllepsis in Larixlaricina: analysis of tree leaders with and without sylleptic long shoots

Abstract

Nonsylleptic and lightly, moderately, and heavily sylleptic leaders with 0 and 1–8, 9–17, and 18–38 sylleptic long shoots, respectively, were cut from 8-year-old Larixlaricina (Du Roi) K. Koch trees. The leaders showed considerable crookedness but degrees of crookedness were not significantly different among leader classes. Leaders of all classes bore sylleptic short shoots. These sylleptic short shoots were largest at midleader locations and larger on leaders with sylleptic long shoots than on nonsylleptic leaders. The terminal buds on many sylleptic short shoots were of long-shoot type. Some sylleptic short shoots with such buds occurred in mid- and proximal-leader positions, whereas lateral buds of the long-shoot type occurred only in distal-leader positions. Sylleptic long and short shoots greatly increased the numbers of leaves on the leaders. This leaf increase occurred principally on the proximal halves of the leaders where leader diameters also increased. Larger amounts of xylem accounted for most of the diameter increases. Subtending leaf to lateral axis distances increased acropetally among lateral buds and sylleptic shoots, but for the latter, these distances were greatest in the middle parts of the respective zones of occurrence. The large variety of developmental pathways for lateral axes on leaders was discussed.