i37 
Xylem of Woody Stems . 
Granted that the Fungus finds in the cellulose a necessary food-element 
and given the existence of layers of this substance in the wood-fibres, 
it follows that the hyphae would proceed in the direction of the source 
of supply, and the delignifying enzyme only comes into play where this 
supply is no longer available. The large amount of cellulose which is 
now shown to occur in the wood, at all stages, having been previously 
unrecognized, the conclusion becomes inevitable that much of the effect 
ascribed to the action of Fungus-hyphae is referable to conditions already 
present, and the action upon the xylem due to any process of sterilization 
must be taken into account when estimating the effect of the penetration 
of hyphae into the wood in culture experiments. 
Without denying the existence of a delignifying enzyme, it is probable 
that the Fungus first attacks the elements where cellulose is already 
present, which would account for the direction in which the destruction 
of the wood sometimes advances. Thus in the formation of partridge- 
wood by Telephora perdix the Fungus attacks certain areas which 
eventually become hollow. Possibly these areas are those in which 
cellulose is present and which, therefore, succumb first, and the hyphae 
penetrate along the line where it is to be found, and the same reason 
may explain why Polyporus sulphureus extends in the direction of the 
annual rings. 
In describing the process of decay in the Oak, due to Polyporus 
dryadeus , Fr., Telephora perdix , M., and Stereum hirsutum y Fr., Hartig 
distinguishes two methods of attack, one accompanied by delignification 
and another in which the conversion of lignin into cellulose does not 
take place. It is conceivable that Hartig may be describing the action 
of these Fungi upon elements already containing cellulose and upon those 
in which cellulose is absent. The fact that in the former method of attack 
the progress of decay is more rapid gives support to this suggestion. 
It appears probable that the occurrence of cellulose in certain areas 
represents a stage of arrested development. The largest distribution of 
cellulose was very frequently observed in the wider annual rings, in which 
the wood appeared to have grown rapidly in a favourable season, and 
the direction of orientation evidently has its influence also. There may 
be some connexion with the phenomenon known to gardeners as the 
‘ ripening ’ of the wood, and in certain seasons when the wood is said 
not to ‘ripen’ it may be an expression of the fact of an incomplete 
lignification. I may mention that I imagine this condition of partial 
lignification may be found to be generally prevalent. Among herbaceous 
plants, for instance in Vicia faba and Oenothera biennis , in the older 
stem-internodes just above the surface of the ground the cellulose lining 
of the wood-fibres is very beautifully shown. 
