Kia. 
FIa. 
Fie. 
ILLUSTRATIONS. 
PLaTeE I, 
. Transverse section of old root, showing continuously thickened endodermis 
and neighboring tissues. 
. Transverse section, 9 centimeters from tip of root, showing young endo- 
dermis, “‘e.” 
. Transverse section of root 4.5 millimeters in diameter, 10 centimeters 
from tip, the hypodermal shell forming. 
4. Transverse section, hypodermal shell of old root. 
. Longitudinal section, cortical parenchyma of young root in 5 per cent 
potassium nitrate, showing wrinkled walls. 
(All figures magnified 160 diameters. ) 
PLATE II. 
. Root 8 millimeters in diameter, 1 centimeter from tip, surface view. 
(160 diameters. ) 
. Same, longitudinal section of epidermis. (160 diameters. ) 
. Same, transverse section. (160 diameters.) 
. An old pneumathode. (1.25 diameters. ) 
. Longitudinal section of young pneumathode: S=stele, Co= cortex, 
Ca=cap. (2.5 diameters. ) 
. Detail, area “x” in fig. 10. (20.5 diameters.) 
. Diagram of small pneumathode, showing relation to loose inner cortex 
of parent root. (20.5 diameters. ) 
. Stellate cells, cortex of pneumathode. (87.5 diameters. ) 
. Thickened cortical cells, base of old pneumathode. (87.5 diameters.) 
PLaTE III. 
. Transverse section of hinge, chlorophyll-bearing tissue indicated by sti- 
pelling. (87.5 diameters. ) 
. Diagram of axis of leaf: A= fibro-vascular bundle, B=schlerenchyma 
sheath, C= upper epidermis and hypodermis, D=green parenchyma, 
E=hinge, F =nether epidermis and hypodermis. (20.5 diameters. ) 
. Upper epidermis, transverse section. (160 diameters. ) 
. Same, longitudinal section. (160 diameters.) 
. Transverse section of stoma. (160 diameters. ) 
. Tangential section, nethermost layer of green parenchyma; contents 
indicated only where bordering an intercellular space. (160 diameters. ) 
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