1914] THOMSON—SPUR SHOOT 381 
made to proliferate after they have undergone one or several winter 
resting periods has yet to be determined. According to my own 
observations, it is much easier to induce a young vigorous tree to 
proliferate than an old slow-growing one, early wounding of the 
tip of the bud of the season being most effective. 
General statement and conclusions 
The lack of definiteness in the number of leaves in a fascicle, 
and the occurrence of supernumerary needles in the recognized 
primitive region and after wounding, are evidence of the branch 
character of the spur of the pines. The normal occurrence of single 
spirally arranged leaves in the seedling, their appearance at times 
on the cone-bearing branch, their traumatic revival in many 
instances in the adult, and the transitions which have been found 
between them and both scale and fascicled leaf, practically demon- 
strate that ancestrally the leaves of the pines were spirally arranged 
on ordinary branches, and that the spur is derived from this con- 
dition. Its normal proliferation in the seedling and young plant 
into an ordinary branch with both primordial and fascicled leaves 
and the traumatic revival of this condition in the mature tree 
place this conclusion beyond reasonable doubt. In all these 
features the pines differ from the other spur shoot-bearing conifers 
only in degree, in conformity with their more specialized condition. 
If in the one case the spur is a branch, it certainly is in the other. 
The pine spur shoot, moreover, is wholly vegetative, while in the 
other forms it is less specialized and combines both the vegetative 
and the reproductive functions, as is the case in Ginkgo, the most 
Primitive of our living spur shoot-bearing forms. 
_ When one comes to compare the conditions in the living pines 
with their fossil progenitors, several important points develop, 
which bear out the branch character of the spur. FONTAINE (9 
has described several species of pines from the Potomac or Younger 
Mesozoic, having had to modify HrEr’s genus Leptostrobus slightly 
for their reception. These remarkable pines had needle-shaped 
leaves “scattered on the larger or principal stems and grouped in 
bundles on the ends of short twigs” (p. 227). Some of the fascicles 
from FontaINE’s work are reproduced in text fig. 2. They bore 
