Concrescent and Solitary Foliage Leaves in Pin us. 21 
tissue which normally separates the bases of the two leaf rudiments. 
The latter would then be continuous, and a concresent structure 
would result, which may be regarded as entirely foliar in origin, 
unless visible indications to the contrary can be adduced. The fusion 
always extends less than half way across the transverse section of 
the double leaf, and, when the bases of some specimens were 
examined, a small papilla, apparently representing the apex of the 
short shoot, was found between the partially fused leaves. 
The orientation of the double leaves is not constant. Cases 
were found in which the leaves were fused by their adaxial margins, 
i.e. the margins directed towards the twig, and away from the scale- 
leaf in the axil of which the spur-shoot with its two foliage-leaves is 
borne (Fig. 2, A). Other cases show fusion of the abaxial margins 
(Fig. 2, B), and obliquely placed-concrescent leaves also occur 
(Fig. 2, C). 
It appears quite probable that the double needles of Sciadopitys 
verticillata may be morphologically similar to those of the Austrian 
Pine described above ; that is they may represent two foliage-leaves 
fused by their margins. On this assumption the two leaves in 
Sciadopitys would be united by their adaxial margins, as shown by 
the orientation of the vascular bundles. Hence the double leaves 
of Sciadopitys would agree, as regards orientation, only with such 
double leaves of the Austrian Pine as correspond to diagram A in 
Fig. 2. Neither a spur-shoot nor a separate apex representing it 
can be recognised in Sciadopitys, so the double needle of this plant 
may be regarded as the result of fusion of two foliage-leaves belong¬ 
ing to a spur-shoot, which has been suppressed. This view was 
held by H. von Mohl. 1 
Other theories must be recognised as tenable, e,g. that of 
Strasburger, 2 who regarded the double needle as the result of the 
concrescence of two leaves with one another and with the apex of 
the spur-shoot. Goebel 3 interprets the double needle as a leaf-like 
twig or phylloclade, bearing on its primordium the tips of the two 
needles as small points. A teratological specimen, which was 
regarded by Bower 4 as giving support to this view, should be referred 
to here. The specimen owed its origin to the proliferation of a cone 
of Sciadopitys, and resembled a double needle at its base, but was 
1 H. von Mohl, Bot. Zeit., Vol. 29 (1871), p. 21. 
2 Strasburger, loc. cit., p. 388. 
3 Goebel, “Organography of plants,” Eng. ed., Part 2 (1905), p. 445. 
4 Bower, Gard. Chron., N. S., Vol. 21 (1884), p. 346 ; see, for figure, p. 282 
of the same volume. 
