448 
BOTANICAL GAZETTE 
[NOVEMBER 
may also be derived from juvenile leaves through such transitional 
forms as bilobed juvenile leaves (figs. 
needles® (fig. 21). 
fossil. 
Fic. 18.—Proliferating logi . ally, 
shoot bearing double 18 tissues 
(bilobed) juvenile leaves. being rec- 
ognized 
from color reactions (see table I). 
Physiology 
Living cells must excrete 
poisonous materials which result 
from the disassimilation process 
(12). In the cells of pines these 
materials are resinous drops, 
which must be gotten rid of. 
In the primitive organs, resin 
probably filtered through the 
epidermis, and the epidermal cells were & 
This is still the 
also secreting cells. 
"IGS. 20-21.—Fi 
contains 2 semi-bu ndles 
note hyp 
(s) on Métal d side of protoxyle 
se concrescent cade ae been considered the homologue of the double 
8 The 
—- of Sciadopit itys 
s shown by arrows in fig. 
, as in typical needles; fig. 21, concrescent or do s 
mal resin canals cite as are typical of juvenile leaves, also inverse WO 
18-20) and concrescent 
Histology 
The chemical nature of the cell walls 
may afford good data for the comparison of 
pine needles with juvenile leaves or with 
phyllodes of other gymnosperms, living and 
Pine needles appear to be more 
differentiated histologically than morpho- 
Fic. 19.—Transverse sec tion of double 
hy S 
usually occur only in needles; 
dermal resin canal typical of Vike: 
leaf; ai deer poesincat obj. 3 
Fic. at 
g. 20, schematic view of fig. 19: note that each vascular strand 
uble needle: 
bored may be homologized with bilobed juvenile leaves bent 
