1914] THOMSON—SPUR SHOOT 373 
injured slightly above the cotyledons the branches which are pro- 
duced in response to the wound bear only primordial leaves. He 
considers that this doubtless occurs in many others. From these 
facts and the stump sprouting, which has been referred to above, 
it seems probable that in all cases the epicotyledonary region, in 
the young plant especially, reverts more readily to the primordial 
type of foliage than the upper parts of the stem, and that what 
seems more or less normal here and, in some cases below the cones, 
can be made to occur in other parts by wounding. Purtxres (23) 
has recorded some observations bearing on this point. Speaking 
of the sprouting of P. chihuahuana after injury by cattle and fire, 
he says (p. 385): “typical sprouting . . . . is confined to trees 
under 5 cm. in diameter (measured at breast height), which send 
up most of the shoots from the root collar or the first 30 cm. above 
ground.” This power of stump sprouting, as it is called, also 
decreases with the size of the stump: “Not a single case was found 
Where the stumps of trees smaller than 7.5 cm. in diameter had 
failed to produce thrifty sprouts, and fully 30-50 per cent of the 
Stumps of trees up to 22.5 cm. in diameter had produced very 
thrifty sprouts, most of the fail stumps occurring between the 15 
and 22.5 cm. classes”’ (pp. 386-387). 
Proliferation of the spur shoot 
The spur shoots, like ordinary branches, arise either in the axils 
of primordial leaves or, when these have been replaced on the stem 
by scale leaves, in the axils of the latter. Unlike the branch, 
however, the spur shoot of the pines increases neither in length 
nor in diameter after the first few weeks, though it may remain on 
the tree with leaves green and apparently functional for many 
years. Thus, primary meristem and cambium are normally 
inactive through by far the greater part of the life of the spur shoot. 
This limited growth of the spur shoot and the production by it of 
only one set of assimilatory leaves which are persistent, not even 
detached on the fall of the shoot, are the distinguishing features of 
the spur of the pines. In the other fascicle-leaved conifers, a new 
Set of leaves is added to the spur shoot each year for many years 
(cf. Ginkgo). There is thus a slight annual increase in length, the 
