MORPHOLOGY OF MEMBERS, 
be accurately estimated by an apical view from above, it must remain uncertain 
whether the position of the mature members is unchanged, or has been altered 
by lateral displacement and torsion of the axis. A displacement, for instance, 
of about 9° would be sufficient to alter the divergence from f to f, a similar 
displacement of 1-3° would change the divergence from to -^-j;- When the phyl- 
lotaxis is very complicated and the number of the longitudinal rows very large, 
extremely small and almost inappreciable distortions are sufficient to destroy the 
original arrangement, and to bring into existence altogether different systems of 
parastichies. This observation is of in- 
terest so far as it makes it seem doubtful 
whether certain complicated phyllotaxes 
are always due to the original arrange- 
ment of the members \ 
(4) It must be observed whether the 
position of newly-formed members or the 
subsequent change shows any relation to 
the direction of the force of gravitation, of 
the light which falls upon them, or of any 
pressure acting from without^. The effect 
of the force of gravitation is that primary 
shoots which are in the main upright put 
forth leaves spreading on all sides ; while 
such as have a decidedly horizontal growth, 
in which a rooting under side is contrasted 
with an upper side, usually show an ar- 
rangement of leaves on the latter in two 
rows, or one which is divided into two 
equal halves by a plane cutting the stem 
longitudinally, as Salvim'a, Marsilea, Poly- 
podium aureu?n, Pteris aquilina, &c. When 
vertical primary shoots with leaves in 
several rows bear secondary horizontal 
branches with leaves in two rows, this 
relationship is less clear, as in the cherry- 
laurel, sweet chestnut, hazel, &c., because 
an influence independent of gravitation 
must in these cases be presumed to be 
exercised by the primary upon the lateral 
axis, as is shown by the position of the 
leaves in the lateral buds before unfolding (see Fig. 155, p. 208). 
(5) It must further be observed whether the first appearance of lateral 
Fig. 154.— Diagrammatic representation of the orthostichies 
of a i phyllotaxis in Pandanus utilis ; A before, B after the 
torsion of the stem. Each of the orthostichies /, //, /// is indi- 
cated by a double Hne ; the genetic spiral is simple; where 
it crosses the orthostichy, the leaf-insertions are indicated by 
figures. 
^ [See Airy, Proe. Royal Soc. /. c] 
^ Hofmeister (Allgemeine Morphologie, §§23, 24) has collected a series of facts which show 
relationships of this kind ; but, both with reference to the individual facts and to the interpretation 
which he gives, I am decidedly of a different opinion, the reasons for which would carry me too far. 
{Vide infra. Sect. 27.) 
