Stem Growth Factors Research Articles

Heartwood and sapwood development and its relationship to growth and environment in Pinus canariensis Chr.Sm ex DC

Pinus canariensis yields a coloured resinous heartwood which has been widely used for centuries in the Canary Islands. Nowadays, although it reaches a high commercial value, very little is known about the influence of environmental, silvicultural and genetic factors on heartwood development in this species. Thus, the influence of environment and stem growth factors on heartwood and sapwood development was investigated in Pinus canariensis 20–200 years old. Samples were taken in natural stands from La Palma and Tenerife islands. The number of growth rings, diameter under bark and radius to the 25th ring were the growth factors most strongly related to heartwood radius. Best prediction ( r 2 = 0.91) for average heartwood radius was obtained with a function of number of growth rings and radius to the 25th ring. Environmental parameters (annual water surplus and influence of Trade Winds) were found to be related more to sapwood width and diameter growth rates than to heartwood width. Stand density, estimated as the number of trees per hectare, was negatively correlated with heartwood and sapwood width, radius to the 25th ring, and average diameter growth rate. It is concluded that good site conditions improve both heartwood and sapwood development in Pinus canariensis.

Physiological studies on light sensitive stem growth

Supplementary radiation given at the beginning of the daily dark period exerts a marked influence on rate of stem elongation of green house-grown plants (Downs, et al., 1957). The influence of this radia tion is dependent on the ratio of red to far-red wave lengths in the radia tion. It is well known that the red/far-red ratio acts directly on the phytochrome pigment system. It may be supposed that the phyto chrome system exerts its effect through one or more stem growth factors. In the present paper it will be shown that some stem growth factor (presumably a hormone) produced in the young leaves and apex is responsible for the red/far-red sensitivity and necessary for normal internode elongation in Phaseolus seedlings.