NOTES 
ABNORMAL PHYLLOTAXY IN THE ASH.— As the suppression of one 
leaf of a pair in the case of a plant with decussate phyllotaxis is a somewhat rare 
phenomenon, a specimen showing this and certain other abnormalities appears to 
be worth describing. 
The specimen referred to is a shoot of the Common Ash (Frcixinus excelsior , L.), 
which Mr. T. A. Sprague kindly handed to me for examination. 1 The shoot had a 
solitary leaf at one of the nodes, and no trace was visible externally of the second leaf 
which would normally be present at the node. It seemed advisable, however, to study 
the specimen anatomically before assuming that total suppression of the second leaf 
had taken place. 
Though the shoot showed considerable vertical displacement of some of the 
leaves, it appeared obvious that the phyllotaxy was fundamentally decussate, there 
being no difficulty in finding the nodal companion of any leaf, except in the case 
of the solitary leaf mentioned above. 
Transverse sections through the node with the single leaf show that there is 
no leaf-trace for a second leaf. Also, instead of the normal broadening of the pith 
into oval or elliptical form as a preparation for the separation of leaf-traces for two 
leaves, the pith here undergoes a one-sided alteration in form, the extension of the 
pith taking place only on the side towards the solitary leaf. 
The position of the solitary leaf is such as would be correct for one of a pair 
decussating with those above and below. In view, however, of the displacement 
of some of the leaves, a further examination of the anatomy of the shoot in relation to 
the phyllotaxy was made, with the following result. Where there is vertical displace¬ 
ment between two leaves which appear to represent a pair, the first preparation 
for nodal structure is normal; i. e. a practically symmetrical broadening of the pith 
takes place, but the succeeding stages, leading to the separation of the vascular supply 
of the lower of the two leaves, are reached earlier than those for the upper leaf. 
The phyllotaxy of the specimen may therefore be described as decussate, 
modified by vertical displacement, and by the suppression of a leaf at one of the 
nodes. The solitary leaf is of normal size and shows no signs of a double nature. 
In the somewhat similar case, however, of a specimen of Rhinanthus Crista-galli 
bearing several alternate leaves described by Groom, 2 a double leaf was present at the 
point of transition from opposite to alternate arrangement, and the phenomenon 
is therefore explained as ‘ one of morphological concrescence or of physiological 
fusion of impulses \ 
1 The shoot was taken from a hedge near Chesham. 
2 Groom : Longitudinal Symmetry in Phanerogamia. Phil. Trans. Roy. Soc., ser. B, vol. cc, 
p. 106. 
[Annals of Botany, Vol. XXIX. No. CXIV. April, 1915.] 
X 1 
