THE ASSIMILATING SYSTEM. 211 
palisade cells (Fig. 128). The assimilating surface is often in- 
creased by a falling off of the membrane (as in the needle-shaped 
leaves of the Conifere). In order to be able to take up the 
products which are formed and to conduct them rapidly, the 
palisade cells are now and then located upon funnel-shaped col- 
lecting cells, which are in connection with the proper cellu- 
lar threads (vascular bundles); the latter running into the 
nerves of the leaves as a much branched radiating system, with 
extremely fine terminations (Fig. 130). 
‘K > s a 
aE ae 
— 
Fig. 128.—Transverse section through a sabre-shaped (centric) leaf of Eucalyptus 
globulus; oe, oil-spaces, with drops of oil; gfb, vascular bundle; s, stomata; k, corky 
growths; c, cuticle (Tschirch). Compare also Fig. 2 a and b. 
The under side of the leaf, which is always ofa lighter green 
color, contains much less chlorophyll than the upper side, and 
is traversed by wide air-canals (spongy parenchyma, leaf- 
merenchyma, Fig. 129 sch). 
The entire interior of the leaf, with the exception of the 
vascular bundles, which is inclosed by the ~ epidermal sides, 
is termed the mesophyll.’ 
1 Mé6os in the middle, pvador leaf. 
