AERATING SYSTEM. 237 
their immersed portions, also show very large and numerous 
intercellular spaces (Rhiz. Calami, Fig. 151, Carex leaves, 
rhizomes of the Nymphea, Carex arenaria and Gratiola’). 
The intercellular spaces produced by the disintegration of cells, 
as a result of the tensions occurring through growth, may 
assume the most varied forms, and finally by far exceed the 
cells themselves in area. 
Excellent examples of this are afforded by the thickened 
margins of Siligua dulcis, the more central tissue of Fructus 
x oe 
ae 
a 
Seam, 
9p rir 
ws 4 
' Fie. 153.—Transverse section through Caryopiytius, inner tissue; f, loose, branched 
cells, interrupted by large air-cavities; ¢, d, fibro-vascular bundles; v, central fibro- 
vascular bundle. 
Aurantiorum (Fig. 152), the rhizome of Calamus and a portion 
of the inner tissue of the clove (Fig. 153). a 
Finally, wide spaces containing air (air-cavities, lacune) may 
also be }found between the tissues, in consequence of the deli- 
cately-walled parenchymatous tissue, especially the medulla, 
not being able in its development to keep pace with the growth 
in thickness of the other tissues, so that the cells of the former 
1 Berg’s ‘‘ Atlas, plate xxii., Fig. 55. 
