124 Potter . — On the Occurrence of Cellulose in the 
On examination of pieces of wood from the same branch, before 
sterilization, I was surprised to find that in many sections a thick layer 
was present in several of the fibres which gave the violet colour character- 
istic of cellulose, when treated with haematoxylin ; and similar sections 
showed a layer in the fibres which refused to react to phloroglucin. Treat- 
ment with iodine and sulphuric acid also gave the characteristic blue. This 
unlooked-for result in apparently sound wood led me to examine a number 
of shoots of Oak of various ages, carefully selected for their vigorous growth 
and entire freedom from disease. 
For the purpose of this investigation it was specially important that 
fresh material only should be used. Pieces of felled wood left in the open, 
even for a short time, would be liable to the objection that any cellulose 
present in the xylem might be due to the process of decay. For this 
reason freshly cut branches were always used and the sections made 
generally, on the day following that on which the material was obtained, 
when it was still fresh and before any change could have taken place. 
Shoots of Oak were selected from trees growing near sheltered river banks 
and from those fully exposed in the open country. At first transverse 
sections were cut by a microtome through stems of varying ages and about 
1.3 cm. in diameter. The sections thus obtained were stained with 
phloroglucin and anilin sulphate, and it was found that in certain areas 
the internal layer of the walls of the fibres refused to act to these stains 
and remained as a white layer inside the otherwise coloured layer, but 
when treated with Schultze’s solution, with iodine and sulphuric acid, or 
with haematoxylin, the characteristic blue colour was at once given by 
this layer. These tests are all confirmatory one of another, and leave 
no doubt that the substance of the inner layer was of the nature of 
cellulose. As haematoxylin alone sufficiently indicated these results 
permanent preparations were made by using Delafields haematoxylin and 
mounting in Canada balsam. 
In transverse section this cellulose layer appeared as a broad violet 
lining, gradually shading off towards the middle lamella, sometimes being 
partially detached and lying kinked in the lumen (see PL VIII, Fig. 2). 
Longitudinal sections confirmed the above observations, the cellulose 
lining being sometimes torn out by the razor and resembling an isolated 
prosenchymatous element. It was noticeable in longitudinal sections that 
around the bordered pits a layer of violet was often present when stained 
with haematoxylin or Schultze’s solution, showing that the bordered pits 
were also surrounded by a ring of cellulose. 
The fibres containing the cellulose lining occurred singly, in isolated 
groups, or in broad bands concentric with the annual rings and interrupted 
by the medullary rays ; but they seldom passed round the whole of the 
stem. It was necessary to cut across the entire stem, for, although the 
