22 Concrescenf and Solitary Foliage Leaves in Pinus. 
forked into two branches above. One of these bore higher up an 
apparently simple needle and also a scale-leaf with a small twig in 
its axil. 
Of the six solitary leaves of the Austrian Pine mentioned above 
three were of quite normal form, and a withered stump of the 
second leaf was found on each of the three spur-shoots. 
The three other solitary leaves were abnormal, being roughly 
cylindrical in form. 1 In two of these a groove was present on one 
side of the leaf, and was continued upwards for some distance from 
the base. It is seen at g in Fig. 3. On following the groove down¬ 
wards in a series of transverse sections, it was found to contain, 
right at the base of the leaf, two papillae, one of which ( a in Fig. 4) 
appears to represent the apex of the spur-shoot, and the other (/ in 
Fig. 4) to be the arrested rudiment of the second leaf. In the third 
specimen the leaf showed no groove except at the extreme base, and 
in this case only one papilla was found. 
In Finns monophylla Torr. the spur-shoots mostly bear each a 
single needle, but two are occasionally present. When the leaf is 
solitary, it is roughly cylindrical, but when two leaves are present, 
each is nearly semicircular in transverse section. Masters 2 found 
by studying early stages that two leaf-rudiments are always 
produced, but that one of them generally becomes arrested at an 
early stage. Hence the solitary leaves of Pinns monophylla are 
strictly comparable with those found on the Austrian Pine. Arrest 
of one leaf on a spur-shoot, which is a rare occurrence in the latter 
species, has become general in the former. 
It is not unlikely that both double and also solitary needles 
may occasionally occur on other species of Pinns 3 besides those 
mentioned here. As the abnormal needles are by no means con¬ 
spicuous among the normal foliage, they are liable to escape notice. 
A double needle of Pinns , like the examples described above, 
may be regarded as being produced by partial fusion of two normal 
leaves, though other views are not refuted. The normal needle of 
Sciadopitys may be somewhat similarly interpreted, but as showing 
more complete fusion of the two leaves, with suppression of the 
spur-shoot and its scale-leaves. Solitary needles, occasionally 
found in some species of Pinns, originate in the same way as the 
typical leaves of Pinns monophylla. 
1 Solitary leaves similar to these appear to have been seen by Strasburger 
(loc. cit., p. 389) in Pinus Pumilio. 
2 Masters, “ Pinus monophylla.” Ann. Bot., Vol. 2 (1888), p. 124. 
3 A few cylindrical solitary leaves ha/e oeen found on a tree of Pinus 
muricata D. Don. 
