EXPLANATION OF THE ILLUSTRATION 
Plate 5. Scanning electron micrographs (SEM) of laboratory prepared pet- 
rifactions of contemporary redwood, Sequoia sempervirens. All four figures 
are transverse fracture sections. Specimen in Figure 4 was ‘etched’ with hot 
nitric acid-potassium chlorate mixture to remove wood substance. 
Fig. | Tracheid lumina infilled with silica deposits. SEM. X2000. 
Fig. 2. Juncture between three tracheids, showing siliceous lens in pit 
chamber (left). Shredded tissue overlying chamber, resulting from fracture of 
the specimen during preparation for microscopy, helped to prevent its loss. 
SEM. X2000. 
Fig. 3. Juncture between several tracheids, showing silica deposits in the 
middle lamella region. SEM. X2000. 
Fig. 4. Lumen casts of tracheids and ray parenchyma cells in the deor- 
ganicized sample. SEM. X 1000. 
