THE SPUR SHOOT OF THE PINES 
ROBERT Boyp THOMSON 
(WITH PLATES XX—XXIII AND TWO TEXT FIGURES) 
Introduction 
The deciduous spur shoot, with its limited growth and per- 
sistent whorled needle leaves, is the distinguishing vegetative 
feature of the genus Pinus. This structure has been generally 
regarded as a specialization, the more primitive form of the foliage 
being indicated by the single spirally arranged leaves which occur 
on the seedling and in some forms on the adult plant after injury. 
JEFFREY, however, has raised the question recently of the primitive 
or specialized character of the fascicled foliage of the pines in his 
work on the phylogeny of the conifers. He states (15, P- 331) 
that the spur shoot is “a primitive attribute of the coniferous 
stock” which “has persisted at least in a vestigial form, in connec- 
tion with the reproductive apparatus, long after it has disappear ed, 
or almost disappeared, in the vegetative axis of the living conifers, 
with the exception of the very ancient genus Pinus.” T his view 
is so entirely at variance with so many foliage features, in both 
the living and fossil forms, that it is difficult to see how JEFFREY 
could have “cast the balance of evidence” in favor of it. Since, 
however, he makes much of this spur shoot argument in present- 
ing his case for the ancestral position of the Abietineae among the 
other conifers, it is desirable to direct attention at least to the most 
important features of the evidence which is opposed to this view: 
The writer (27) has already stated, in a brief and general way: 
some of these features, in a paper dealing with the relative antiquity 
of the Abietineae and the Araucarineae, from the standpoint of 
their anatomy. New material, however, has recently come to hand 
which has prompted this more extended treatment of the subject. 
The literature has also been thoroughly canvassed for information 
on the spur of the pines. 
Of the conifers there are four genera with fascicled leaves: 
Cedrus, Larix, Pseudolarix, and Pinus. In the first three of these 
Botanical Gazette, vol. 57] [362 
