1914] THOMSON—SPUR SHOOT 363 
the leaves are numerous, while in Pinus they are much more 
restricted in number, not more than 8 having been recorded up 
to the present. In the former, too, the number is indefinite and 
the leaves are spirally arranged, while in Pinus the definite cyclic 
arrangement has been established. A parallel to this is seen in the 
angiosperm flower, where the lower forms of both monocotyledons 
and dicotyledons have an indefinite number of floral parts in a low 
spiral, while in the higher forms the number is definite and the 
arrangement cyclic. The spur shoot of Pinus is deciduous in the 
second to the twentieth year (ELwEs and HENRY 7, p. 1002), and 
its leaves fall with it, remaining permanently attached. In the 
other genera it is the spur shoot which is persistent, and the leaves 
are cast either annually or in the second to the fifth year. The 
small and more or less definite number of persistent and whorled 
needle leaves and the regularly deciduous character of the spur 
shoot are features which render this structure in the pines very 
unlike the ordinary branch and also unlike the spurs of the other 
forms, which differ from an ordinary branch only in their limited 
primary and secondary growth. The features that will receive 
attention in this paper are such as indicate the branch character 
of the spur in Pinus. 
Number of needles 
The number of leaves in the fascicles of the pines, appearing 
on first sight constant, and being, as ENGLEMANN says (8), “the 
most obvious distinctive character,” has been extensively made use 
of in their classification. He states (8, p. 161) that “the sections 
of 2-leaved, 3-leaved, and 5-leaved pines were the only ones known 
to the older botanists”; to these were added two other sections 
“by Linx (Linnaea, 1841), one with 2 or 3, the other with 3 or 4 
leaves in a sheath.” Subsequently forms with single leaves and 
others with 3-5 leaves in the fascicle had to find a place. Numerous 
exceptions to this classification have also been recorded. Kron- 
FELD (16, p. 68) gives a summary of the variation in many different 
species observed up to the date of his article. He cites, for example, 
the occurrence reported by REICHARDT of 3, 4, and 5 needles = 
oe silvestris, which is normally bifoliar, and also of 3, 4, and 6 in 
