1918] DUFRENOY—PINE NEEDLES 445 
2-needled spur shoots, or vice versa (14). These bud mutations, 
like proliferating spur shoots,’ are due to modifications in the 
normal nutrition of the pine, caused by environmental factors, 
traumatisms, and chiefly parasites, and they result in increase of 
Osmotic pressure in differentiating tissues. 
That osmotic pressure is the ultimate determining factor is 
demonstrated by the fact that we were able to force 7-year old 
P. maritima to produce 3-needled spur shoots or proliferating spur 
shoots by watering abundantly, which of course increased tur- 
Fic. 9 
Fics. 9-10.—Fig. 9, protoxylem in first needle appearing on juvenile pine: w, 
cells whose walls begin to show lignification and stain red with phloroglucin; fig. 10, 
protoxylem in very young needle of juvenile pine: section near apex; only one 
xylem pole 
gescence of cells. Whether needles or juvenile leaves develop 
depends upon the relative supply of soluble osmotic material to the 
cells. Needles, or all adult organs in general, develop from material 
obtained from the earth and atmosphere, by gradual assimilation. 
Juvenile leaves, or all juvenile organs in general, develop from 
material stored in the reserve tissue (9). 
TRANSITION FROM JUVENILE LEAVES TO NEEDLES.—As needles 
and juvenile leaves are but different responses of the same organism 
to environmental factors, they may be assumed to show transitional 
° Development of lateral long shoots is exaggerated on pine seedlings exposed to 
sea wind, and results in “buissornement,” like that recorded by Devaux (6) for Erica 
on ocean dunes 
