210 PLANT ANATOMY. 
The surface of the leaf which is chiefly exposed to the’ light 
becomes the assimilating side. With bifacial * leaves, that is, such 
as are flatly expanded, and the upperand under surface of which 
is differently developed (as in the heart-shaped Fol. Eucalypti, 
Figs. 2 b, 127, 129, Lactuca Sativa), this is the upper surface; 
with centric leaves, that is, such as are placed vertically, and both 
sides of which are equally constructed (Fol. Eucalypti, sabre- 
shaped, Figs. 2 a, 128, Lactuca Scariola), it is both sides. 
The cells of the assimilating side, which is always of a darker 
green color, are replete with numerous chlorophyll granules, 
located along the walls, and are extended ina palisade-like man- 
Ss /0e ‘S 
Fic. 127.—Transverse section through a heart-shaped (bifacial) leaf of Eucalyptus 
globulus; oe, oil-space; s, stomata; w, undersurface; 0, upper surface. After Tschirch, 
Pharm, Zeit., 1881, No. 88. , 
ner more or less perpendicular to the vertical axis of the leaf 
(Figs. 96 g, 127, 128, 129 pal, palisade * parenchyma). 
The special development of palisade parenchyma remains un- 
_affected only in typical shade-plants.* On the other hand, in 
- all centrically constructed leaves, both sides are provided with 
' Bis, twofold, and facies, side. 
* From the French word palissade, and this from the Latin masculine 
palus (not pallus !), therefore not pallisade, as it is often incorrectly 
written. (This applies more especially to the German orthography. 
F. B, P.) 
* Globularia Alypum L. and other species present a notable example 
of an homogeneous leaf tissue without a palisade layer. 
