L. A. Boodle. 
1 9 
CONCRESCENT AND SOLITARY FOLIAGE LEAVES 
IN PIN US. 
Bv L. A. Boodle, F.L.S., 
Jodrell Laboratory, Royal Gardens, Kew. 
[With Four Figures in the Text.] 
BNORMAL specimens showing concrescence of the two needle 
leaves on a spur-shoot were discovered by Strasburger 1 in 
two species of Pinus ( P. Puinilio and P. sylvestris), and were 
described by him in connection with his interpretation of the 
morphology of the double needles of Sciadopitys verticillata. 
A similar abnormality has been found on a tree of Austrian 
Pine 2 growing in the Royal Botanic Gardens, Kew. Most of the 
foliage of this tree is normal, but pairs of concrescent leaves are 
produced every year in fair numbers. 
The nature of the fusion between the two leaves is illustrated 
by the transverse section shown diagrammatically in Fig. 1. This 
section was cut near the base of the double leaf, viz. at a height of 
4 mm. above the basal sheath of scales. The structure is identical 
with that of two normal leaves of the same species, except for the 
differences immediately connected with the fusion, the mesophyll 
of the two leaves being continuous at m, and the epidermis and 
hypoderm ( ep. hy.) respectively being continuous on either side of 
vi. The fusion described above may be continued from the base to 
near the apex of the two leaves, but never quite to the apex, two 
free leaf-apices being always present. At a short distance below 
the point at which these tips become free, the tissue connecting 
the two leaves shows a decrease in breadth, which continues until, 
in the last transverse section showing concrescence, the leaves are 
only united by one or two epidermal cells at the extreme margin. 
Measurements of twenty-five specimens of double leaves gave 
9'5 mm. as the average length of the free portion, and 89’0 mm. for 
the concrescent portion. In one case the free part was only 1 mm. 
long, and in another case it was 47 mm. long, these being the two 
extremes observed. 
The examination of a considerable number of twigs on the tree 
on which the abnormality was found, gave the result that one or 
more double needles are present among the tuft of needles at the 
end of nearly every twig. The leaves on the spur-shoots on six 
1 Strasburger, “ Die Coniferen und Gnetaceen,” 1872, p. 387. 
2 Finns Laricio Poir. var. nigricans Pari. (=P. Laricio var. austriaca Endl.) 
