Photoperiodic Control of Leaf Growth and Cambial Activity in Pinus sylvestris

Abstract

IT has long been known¹ that geographical races of Pinus sylvestris from northern latitudes show reduced growth of the shoot when planted in more southern localities. Sylven² and Langlet³ suggested that this is probably a photoperiodic effect, arising from differences in the natural length of day between different localities. My experiments have shown that Pinus sylvestris is indeed photoperiodic. As in many other species⁴, short photoperiods (10 hr.) induce earlier cessation of growth of the shoot in first-year seedlings of P. sylvestris as compared with long photoperiods (15 hr.), so that fewer leaves are formed before the formation of a terminal resting-bud. There is also a reduction in the length of the 'internodes', leading to a rosette type of growth, under short days.