140 Potter. — On the Occurrence of Cellulose in Xylem. 
EXPLANATION OF FIGURES IN PLATE VIII. 
Illustrating Professor Potter’s Paper on the Occurrence of Cellulose in Xylem. 
Fig. 1. Transverse section of a young stem of Quercus, diameter 1-3 cm. The shading extending 
partially round the stem indicates the regions of cellulose distribution. 
Fig. 2. Transverse section of wood-fibres from a stem of Quercus, cut when fresh and stained with 
Delafield’s haematoxylin. The lignified layers are yellow and the enclosed gelatinous thickening 
layer violet. Zeiss D., Oc. 4. 
Fig. 3. Portion of a transverse section from the stem of Fagus, cut when fresh, showing the 
inner gelatinous layer present in some wood-fibres, coloured violet. Zeiss D., Oc. 4. 
Fig. 4. Longitudinal section from the wood of Salix , cut when fresh and stained with chlor-zinc- 
iodine. Showing the margins of the bordered pits stained blue. 
Fig. 5. Transverse section of wood-fibres from the stem of Fraxinus, cut when fresh and stained 
with chlor-zinc-iodine. The yellow walls show a complete lignification with no internal cellulose 
layer. 
Fig. 6. Similar section from the same stem of Fraxinus , after boiling on four consecutive days 
and staining with chlor-zinc-iodine. The lignified parts of the walls remain yellow, while the inner 
swollen layers are coloured violet, having undergone delignification. 
Fig. 7. Transverse section from a stem of Aesculus , steamed for two hours on three consecutive 
days, stained with Congo-red, and mounted in Canada balsam. The inner delignified layer of the 
fibre- walls is stained red and lies detached, swollen, and crumpled in the lumen. 
Fig. 8. Transverse section of the wood-fibres from a stem of Quercus after steaming three times, 
stained with chlor-zinc-iodine. Showing the advancing process of delignification due to the action 
of boiling water. 
