1914] THOMSON—SPUR SHOOT 375 
the other genera, and have escaped observation to a great extent. 
Several instances, however, are on record. ENGELMANN (8, p. 
167) says: “in exceptional cases and as a monstrosity the leaf 
bundles may become proliferous, the branchlet which bears the 
secondary leaves elongating and forming a regular branch.” 
Masters (19, fig. 9 and p. 267) figures a pine, with two needles, 
in which the fascicle is ‘prolonged into a shoot with primary-leaves 
and leaf buds.’ Neither ENGELMANN nor Masters mentions 
the species concerned, nor in either case do they indicate the con- 
ditions which have induced the proliferation. Dickson (6) and 
MEEHAN (22) both observed that in P. silvestris proliferation 
occurred as a result of injury. Dr1cKson’s specimen was a twig, the 
extremity of which had been destroyed. He says (p. 260): “the 
development of these buds is stronger the nearer their position to 
the seat of injury.”” The lower ones are merely closed buds, but 
the upper ones “develop well marked foliage leaves, and, in the 
very strongest ones, these foliage leaves have secondary bifoliar 
Spurs developed in their axils.’ In the development of foliage 
leaves spirally arranged ‘on the prolonged axis of the stimulated 
spur,’’ Dickson notes “a reversion to the early or unspecialized 
condition.” MEEHAN’s (22, p. 82) ‘specimens were Scotch pine 
that had been “headed back.” Previous to his observation of 
these proliferating spur shoots, he had been so influenced by von 
Mout’s work on Sciadopitys that he was inclined to consider the 
fascicled needles of the pine as cladodes. He now subscribed to 
the current view and recognized that the whorled needles are leaves 
and that the fascicle is an “arrested branch, having a dormant bud 
at the apex.” BortHwick (2) has observed numerous instances 
in a plantation of P. Laricio and P. silvestris, and has studied the 
conditions under which they develop, as well as the character of 
the resulting branch. He considers that “the interfoliar bud 
develops only under the stimulus of an increased supply of nutri- 
ment,” and instances several kinds of wounding which result in a 
reater advention of food material. In this he agrees with Hartic’s 
explanation of the development of dormant buds. He considers 
that the branch produced from the development of the interfoliar 
bud may bear either primary or fascicled leaves, “the results 
