E. Nicolini, New observations on morphology of beech growth units (Fagus sylvatica L.) - Shoot symmetry, reflection of tree vigor, CAN J BOTAN, 78(1), 2000, pp. 77-87
Citations number
29
Categorie Soggetti
Plant Sciences
Journal title
CANADIAN JOURNAL OF BOTANY-REVUE CANADIENNE DE BOTANIQUE
Beech has a rhythmic growth pattern, each annual shoot being made of a spri
ng growth unit (u.c.), sometimes followed, a few weeks later, by a summer g
rowth unit. Spring u.c. shows an alternate distic foliar distribution, wher
eas summer u.c., according to some authors, shows an alternate spiralized f
oliar distribution. Following morphological and histological observations o
f the buds formed at different periods of the year, it appears that the fol
iar distribution pattern in beech does not evolve from one u.c. type to the
other: foliar primordia are always distributed along two parallel straight
lines, close to one side of the stem, following a "plagiotropic distic" pa
ttern. However axial symmetry of a u.c. can change during its elongation, e
volving from a bilateral symmetry toward a secondary radial symmetry. This
evolution results from a nodal reorientation produced by a twisting of the
internodes, the most significant shift of foliar organs coming from the lon
gest u.c.'s at the level of their longest internodes. It is possible to lin
k u.c.'s degree of development with tree architecture. The less vigourous t
rees (very young or growing under a dense forest canopy) show a more or les
s leaning main axis, formed by less developped u.c.'s, with a bilateral sym
metry; main axis is plagiotropic bearing a flat crown. On the other side, t
he most vigourous trees (adults or on favourable forest sites) show a verti
cal main axis, formed by relatively long u.c.'s, with a radial symmetry; ma
in axis is orthotropic with a well and widely distributed crown.