1914] ; THOMSON—SPUR SHOOT 369 
single-leaved pine, P. monophylla, wounding increases the number 
of needles to two. Figs. 5 and 9 are from a young tree which was 
normally monophyllous. Both twigs were injured just as the 
leaves were starting to develop. On the first, three bifoliar spurs 
have been produced, and on the second, one. I have not observed 
an increase in the ‘number of needles by wounding in any other 
forms, but it is probably of quite general occurrence in the 
pines. 
Before leaving the subject of the number of leaves in the fascicle, 
a peculiar and probably a specialized condition, which has been 
reported in several species, must be referred to. In P. Nelsoni, 
SHAW (26, p. 8) states that the leaves are “connate in fascicles of 
3,’ and that this condition is found even in the seedling. In P. 
Thunbergii the leaves are in twos, while “in var. monophylla the 
two leaves in the cluster coalesce”’ according to ELwEes and HENRY 
(7, p. 1143). These authors also refer to two other cases of fusion 
of the leaves; to CarRrtERE’s (Conif. p. 398, 1867) description of 
a variety (monophylla) of P. excelsa: “each sheath with apparently 
only one leaf, all of the five leaves being welded together”’ (p. 1011), 
and to a monophyllous variety of P. Strobus described by TUBEUF 
in 1897, “‘a variety with the needles more or less cohering through- 
out their length, and forming a single needle” (p. 1026). It is 
hecessary to distinguish this spurious monophyllous condition, a 
result of compounding, from the truly single-leaved condition in 
the one species, P. monophylla, which as MASTERS (20) has shown 
arises from the “arrested development of one of its two original 
leaves” (p. 126). 
Scale and primordial leaves 
Below the persistent whorled needle leaves on the spur shoots 
are spirally arranged scale leaves, which are homologous with the 
similarly though more laxly arranged scale leaves on the ordinary 
branches. They are either persistent or deciduous. On seedling 
stem and branches scale leaves are replaced by the so-called pri- 
mordial leaves, which are a prominent feature in the pines. These 
Seedling leaves, as Coutrer and CHAMBERLAIN (5, p. 222) have 
noted, are of simpler structure than the whorled needles. There 
