EXPLANATION OF THE ILLUSTRATIONS 
Prare V. Fie. 1. Transverse section of an unidentified fos- 
sil wood of Cretaceous age. The wood is an intensely silici- 
fied organic residue of the original woody tissue. The cell 
wall layers retained closely resemble the cellulosic residues 
of anaerobically degraded wood as shown by comparison with 
Plates I and II. Ground section. » 182. 
Kia. 2, Same specimen as shown in Fig. 1, but more highly 
i y @6y. . ry : . 
magnified. Note the “lignin’’ residue of the secondary wall. 
732. 
Fig. 38. Robinia Pseudo-Acacia LL. Portion of vessel wall 
showing structure of the vestured pits. The vestured portion 
of the pit consists of primary wall. ~< 1532, 
hic. 4. Robinia sp. Silicified wood from the Tertiary of Mon- 
tana. Portion of vessel wall showing retention of structure 
of the vestured pits. Compare with normal wood of Robinia 
Pseudo-Acacia L. shown in Fig. 8. Ground section. 860. 
Fie. 5. Same specimen as shown in Figs. | and 2, but with 
varying degrees of degradation of the cell wall previous to 
silification. Ground section. 732. 
Kia. 6. Tangential longitudinal section of same specimen as 
shown in Fig. 4. The beaded structure of the more resistant 
primary wall is preserved as an organic residue, consisting 
of modified lignin and embedded in silica. Ground section. 
225, 
Fig. 7. Same as Fig. 6, except more highly magnified. 
Ground section, » 860, 
