Xylem of Woody Stems. 123 
diversidens , he mentions the most internal, somewhat gelatinous layer of 
many healthy Oak wood-fibres, which colours blue with chlor-zinc-iodine. 
He evidently regarded the character as so limited as to be negligible, and 
the fact as noted by him appears to have escaped attention. 
Strasburger (’91) in the ‘ Leitungsbahnen ’ mentions incidentally that 
the inner thickened layer of the wood-fibres of Robinia pseudacacia colours 
violet by potassium iodide ; and also that in Wistaria the wood-fibres show 
an inner thickened layer, sometimes almost completely closing the lumen, 
which on treatment with potassium iodide and with chlor-zinc-iodine gave 
a beautiful wine-red colour. 
In the case of Pinus sylvestris it has been shown by Schellenberg (’96) 
that the primary medullary rays remain unlignified until the third year 1 . 
He has also observed that among the wood-fibres generally the middle 
lamella is very often more lignified than the other layers, but that com- 
pletely unlignified inner lamellae are only seldom met with, as in Trio se turn 
perfoliatum . 
With these exceptions I can find no reference 2 to the presence of 
cellulose in mature wood, except as the result of the destructive action of 
certain Fungi. Abromeit (’84) mentions that after the use of chlor-zinc- 
iodine he has been unable to detect the tertiary gelatinous layer in the 
wood-fibres of the Oak, and, so far as I have been able to trace, it has 
come to be very generally accepted that the elements of the wood become 
entirely lignified, using the term in its simplest acceptation. 
After an extended examination of a very large series of specimens 
I have detected the presence of cellulose in the xylem of many trees as 
a normal condition in perfectly healthy and vigorously growing stems. It 
occurs chiefly in the wood-fibres, and proves to be by no means an excep- 
tional occurrence. 
My attention was first drawn to this question when studying the 
action of a Bacterium ( Pseudomonas destructans) (’99) upon the cell-walls 
of storage tissues, such as in Turnip, Carrot, &c., and following up some 
investigation into the destructive action of this parasite upon the xylem. 
Small pieces of the xylem of Quercus and Fagus were sterilized by steam- 
ing in test-tubes in which they were half immersed in water, and afterwards 
were sown with a pure culture of this Bacterium. After an interval of 
fourteen days transverse sections showed a very marked presence of 
cellulose, as indicated by chlor-zinc-iodine and haematoxylin. As this 
seemed to suggest an action by the Bacterium corresponding to that of 
the Fungi above mentioned, it became necessary to determine whether this 
cellulose was present before inoculation. 
1 I have observed cells in the medullary rays remaining unlignified for a much longer period. 
2 De Bary (Comp. Anat., Engl, ed., p. 482), quoting Sanio, mentions the occurrence of this 
gelatinous layer, which remains unlignified. 
