180 
THE FLORIST’S JOURNAL. 
of all leaves is alternate, and the whorls of opposite leaves, 
which sometimes occur, result from the contraction or non¬ 
development of the internodes. The true position of leaves, 
with reference to the stem, appears to be that of an elongated 
spiral, and in many trees this direction can be readily traced; 
as, for example, in the genus Pinus, and more particularly in 
Pandanus, which, in consequence of such a distribution of its 
leaves, is named the Screw Pine. The apparently irregularly 
arranged leaves of an Apple, a Willow, or almost any common 
tree, will also serve to illustrate the same ; for if a line be drawn 
from the base of one to that of the next above it, and continued 
upwards, it will be found to have described a true spiral: it 
may also be remarked, that those leaves which are usually op¬ 
posite betray a manifest tendency to become alternate, or thus 
revert to their normal position. This question may, however, 
be carried to a much greater length, and the spiral direction of 
leaves may be proved mathematically; even the particular 
nature of the spires,, with reference to individual species, have 
been ascertained to be subject to fixed laws, which admit of 
definition. Brunn, a German botanist, has published an ela¬ 
borate memoir, in which he has thrown much light on this 
interesting subject; and among our own countrymen, Professors 
Henslow and Lindley may be mentioned, as having particularly 
directed their attention towards it. The observations and 
remarks of Professor Henslow, which are deserving of the 
greatest deference, have very much simplified what at first 
might seem to be obscure; the scales of a fir cone, which are 
only pistillary leaves, developed around a changed stem, he has 
demonstrated to have a spiral arrangement, by very instructive 
diagrams and mathematical calculations; for these, which are 
possessed of much interest, I must refer to his remarks on 
“ Structural and Physiological Botany/’ which form part of the 
“ Cabinet Cyclopaedia.” I pass over this part of the subject the 
more readily, in consequence of its near relation to the doctrine 
of Morphology, which a brother member has undertaken to 
explain. 
October , 1843. 
( To be continued .) 
