THE PHYLLOTAXIS OF THE DATE PALM (PHOENIX ... - Pubhort.org

._n ___ _ -- - _..'--Fig 8: leaf winding and deviationThe first characteristic is what few authors have taken inconsideration and called the leaf winding (Toutain, 1979). A rightdefinition of this parameter is not easy. We must consider two plans todescribe it: one plan is constituted by the axis of the leaf(cental basalportion of the rachis) and the vertical axis of the date palm at the base andthe centre of the leaf; the other plan is the medium plan of the leaflets (leafplan). This last plan is more problematic because, with the growth and theageing of the leaf, it differs from the low leaflets to the terminal ones andloses its plan appearance with the increasing curving of the leaf. Mostgenerally the angle between these two plans is not right but the leaf planwinds to the left or to the right.The second characteristic concerns the end of leaf rachis. As probablya mecanical consequence of the winding of the leaf, the last portion of theleaf rachis is gep.erallynot straight but curved in the same direction as thewinding. I gave to this leaf morphological characteristic (usefull regardingphyllotaxis and, according to my information, never mentioned till now)the name "deviation" to avoid confusion with the leaf curvature (Nixon,1950).I have established the direction of the winding angle and of thedeviation of the leaves of the 2000 date palms studied. I have found that,for each of the date palm observed, all the leaves close to the spire (centralspear shape leaves), excepted few leaves sometimes, presented the samewinding and deviation direction,. Very often, this is also true for all theleaves of the same date palm.568- - - - - - --