BACTERIA. FUNGI. 167 



wood is destitute of tannin. It is natural to suppose, therefore, that the mycelium 

 takes away and uses up the tannin. It has also been observed that wherever the 

 hyphse of the Pine-blister (Peridermium Pini) ensconce themselves, the nitrogenous 

 parts of the protoplasm and the starch vanish, whilst turpentine remains behind, 

 clinging in drops to the inner walls of the cells. These are, to be sure, very sparse 

 data ; but they show that the entire cell-contents are not absorbed by the parasite 

 unaltered, or used in that condition as material for the building up of its own body. 



Not only the contents of the cells preyed upon, but the walls as well, are partially 

 used as food by the hyphse which penetrate into the woody axes of arborescent 

 angiosperms and gymnosperms. The mycelium of several species of Polyporus and 

 Trametes begins by bringing the lignin in the cell-walls into solution, leaving 

 nothing but a pale-coloured cellulose wall. Soon afterwards, the so-called middle 

 lamella, which connects adjoining wood-cells, is also dissolved, and the colourless 

 wood-cells, now almost like asbestos-fibres in appearance, fall apart at the slightest 

 touch. When the wood of a larch has been infested by the mycelium of Polyporus 

 sulfureus, there are always deep furrows running obliquely on the internal walls of 

 the wood-cells; this loss of substance, too, can only arise from the solution, and 

 absorption as nutriment, of parts of the walls by the action of the hyphse. 



All decompositions and alterations of structure of the above kind within the 

 precincts of the host's cells are naturally followed by a disturbance of function, and 

 ultimately by death. The entire plant is, however, but rarely killed by parasites 

 belonging to this group. The decomposition by bacteria of a mammal's blood, 

 though at first confined to a particular part of the body, spreads in a moment 

 throughout the whole organism, owing- to the heart's action and the circulation of 



o 0*0 



the blood. But the decomposition taking place in the manner just described, 

 through the intervention of hyphse, propagates itself, on the contrary, only very 

 gradually from the cells immediately attacked to their neighbours, and it gets 

 weaker and weaker as the distance from the site of the invasion increases, a 

 circumstance to which we shall recur later on when discussing the phenomena of 

 fermentation and decay. The nature of the parasite and the power of resistance of 

 the host have an undoubted influence on the rate of distribution. In many cases 

 alteration is limited to the cells attacked and those immediately adjoining, so that 

 the area destroyed is circumscribed. It is manifested on fresh green leaves, often 

 merely in the form of small, isolated, yellow, brown, or black spots and patches, 

 which only slightly interfere with the activity of the leaf, and do not cause it to 

 change colour, wither, or fall off any earlier. In other instances, however, the 

 entire leaves and stem do undoubtedly become flaccid and shrivelled and dried up 

 into a black mass, looking as though they had been carbonized; or else putrefaction, 

 such as that which is excited by bacteria, invades the whole mass. 



As above stated, when the wood in the trunks of trees is perforated and 

 consumed by hyphse it is resolved into fragments. It becomes rotten, takes the 

 form of an asbestos-like or crumbling and pulverulent mass, and is then obviously 

 no longer capable of fulfilling its various functions in the living plant. If the 



