1 38 Potter . — On the Occurrence of Cellulose in the 
Summary. 
1. It is found that a gelatinous thickening layer which reacts at 
once to the various colour-tests for cellulose occurs very commonly, though 
very irregularly, in the fibre-walls of the xylem as a normal condition in 
a great number of perfectly healthy trees, in all localities and situations. 
It may have a very partial distribution, or may occur very generally 
and conspicuously through the stem, and may be present only in parts 
of the same annual ring. Sometimes this innermost layer is represented 
only by a thin lining, at other times by a very broad band which appears 
swollen and occupies a large part of the lumen. 
A margin of cellulose is also often present round the bordered pits. 
2. A delignification of the xylem is effected by the action of boiling 
water, which removes substances which impregnate the cellulose and 
react to the lignin stains, leaving a basis of cellulose as indicated by 
the reactions to the various colour-tests. This is shown by submitting 
thin sections of wood to the action of boiling water, and is confirmed 
by the fact that ether removes from the watery extract obtained from 
sawdust and fragments of wood a substance which reacts to lignin tests. 
Further, cold water, operating for a longer period, has a similar power 
in extracting from the xylem a substance which reacts to phloroglucin 
and thallin sulphate, and thus by continued soaking in water wood under- 
goes a partial delignification. 
A substance showing a blue-green colour with phenol- HC 1 , the test 
for coniferin, is apparently not extracted. 
3. It is demonstrated that the ‘ lignin ’ substances extracted from 
the xylem by water are destroyed by certain micro-organisms, and that 
these flourish more vigorously in the sap-wood than in the heart-wood 
extracts. This latter point suggests that the heart-wood contains some 
substances not readily attacked by Fungi or Bacteria, and accounts for 
the fact of its greater durability. 
4. The presence of this unlignified layer in the wood-fibres probably 
represents a stage of arrested development. Its general prevalence having 
been overlooked, the conclusion is inevitable that the occurrence of cellulose 
which has been attributed to the action of Fungi must to some extent 
be ascribed to conditions already present, and the effect of any method 
of sterilization must also be taken into account. The delignification 
cannot be entirely attributed to an enzyme secreted by Fungi. 
Postscript. 
Since the above was written I have examined the roots of Lupinus , 
Phaseolus, Polygala Senega and Aesculus, and have found the cellulose lining 
in the fibres very distinctly shown in all these cases. Doubtless fibres 
remaining partially unlignified are of quite common occurrence in roots. 
