Spatial arrangement of lateral buds at the time that they form on leaders of Picea and Larix

Abstract

Lateral buds were formed on Piceasitchensis (Bong.) Carr. leaders in April–May before the leaders emerged from the winter buds. At that time, the lateral buds seemed to be evenly (not randomly) dispersed over the cone-shaped surfaces of the parent leader buds. This observation was confirmed and extended by defining the positions of lateral buds on fully extended leaders of P. sitchensis, P. abies (L.) Karst., P. omorika (Pancic) Purkyne, and Larixdecidua Mill. and 'theoretically' telescoping the leaders to their probable shapes in April–May by using computer simulations. It was concluded that the centres of cell division which preceded lateral bud formation were positioned by inhibition–competition mechanisms. This explained why (a) the numbers of lateral buds were related to the sizes of the parent shoots, (b) lateral branches were dispersed with equal expectation in all compass directions, with minimal mutual shading, and (c) a variety of staggered and whorled branch arrangements could occur on leaders of different trees, as long as each whorl was associated with a branchless zone.