pared from untreated specimens of unmineralized wood. 
Moreover, applicability of the technique is not restricted to 
woody tissue alone. It has been used successfully with other 
forms of plant tissue, including cotton fibers, fungi (Agaricus 
campestris and Polyporus betulina), and an algal mat (Figs. 6 
and 7, Plate 3). 
The micrographs appearing in Plates | through 6 are fully 
described in the explanatory texts accompanying each illustra- 
tion. A few additional comments appear below and in the 
following section. 
The siliceous deposits formed within the contempory woods 
by treatment with ethyl silicate have a particulate texture under 
high magnification (see lumen casts in Fig. 4 of Plate |, Figs. | 
and 4 of Plate 5, and Figs. | and 2 of Plate 6), which conforms to 
the dense variety of silica observed by Scurfield et al. (1974) in 
the ray parenchyma cells of some living plants. This particulate 
texture appears to diminish with increasing proximity to wood 
substance. 
Also, the parallel series of siliceous rungs appearing on the 
silicified wall of the vessel element lithomorph pictured in 
Figure 3 of Plate 4, and the siliceous deposits in the pit cavities 
of the ray parenchyma cells shown in Figure 4 of the same 
plate, are two additional features which have been observed by 
Scurfield et al. (1974) in the tissues of certain living plants. 
As suggested by these authors, perhaps the natural deposi- 
tion of amorphous silica in the vascular tissue of certain plants 
may represent the very earliest stages of the petrifaction proc- 
ess occurring in non-living wood and may provide some infor- 
mation into the mechanism of the process. 
II]. A PHysicAL MODEL OF THE 
SILICIFICATION SEQUENCE 
The inferred mode of emplacement of silica, with respect to 
histological detail in wood, during the incipient stages of the 
process, is schematically depicted with the model in Plate 7. In 
this illustration, wood substance is portrayed in white, and 
silica in black. Figure (a) represents a portion of two adjacent 
tracheid walls, including a bordered intercellular pit-pair, of a 
specimen of wood prior to mineralization. The torus, which is 
16 
