428 Prof. H. Marshall Ward. The Relations between 



The next question which arises is — Is there any definite body in 

 the extract that conld kill the protoplasm, and which would not be 

 destroyed by the short boiling ? The answer to this question is 

 simple : the byphee of the fungus develop large quantities of oxalic 

 acid* in the substratum, and this is a substance which is peculiarly 

 poisonous to the living protoplasm of higher plantsf if present in 

 any large quantity. In the normal cells of plants rich in salts of 

 oxalic acid (Oxalis, Begonia, &c.) I need only remind you that the 

 acid is not in the protoplast, but is kept strictly isolated from it by 

 the vacuole wall, as is clear from the researches of Pfeffer and De 

 Vries. 



It is at least conceivable, therefore, that the hypha? kill the cells by 

 flooding the protoplasm with oxalic acid ; but it is not certain that 

 they do not excrete a more subtle poison of the nature of a ferment. 



In any case, it is a significant fact that the hyphse kill the cells by 

 emitting some soluble poison which causes the protoplasm to collapse, 

 and then to turn brown, clearly because it destroys its power of re- 

 taining and restraining the sap in the sap-cavity ; the latter there- 

 fore escapes through the now permeable dead or dying protoplasm, 

 and owing to its acid contents, chromogenes, &c, stains it and the 

 cell-walls brown as the oxygen of the air enters into combination. 



There is thus, from the very first, a struggle between the hypha of 

 the fungus and the cells of the host ; the hypha is in the position of 

 an attacking party, which has to overcome, first the outworks, in the 

 shape of cuticle and cell- wall, and secondly the real fighting force — 

 the protoplasm. 



I take it that the attacking hypha (invigorated by previous 

 culture, as said) excretes various zymase-like substances formed in its 

 metabolism ; one of these succeeds in overcoming the resistance 

 afforded by the cuticle^ and then the cell-wall is penetrated : 

 the partially victorious hypha then advances in the cell-wall, 

 and is nourished by the cellulose which it goes on dissolving, 

 and under its changed conditions of life excretes in increasing 

 quantities yet another zymase or some kind of poison which diffuses 

 to the protoplasm. Now comes the real tug of war — so long as the 

 outer layer of the protoplasm (the ectoplasm) is in a position to 

 refuse access to, or in any way to destroy, the poison, the rest of the 

 protoplast remains impermeable, and the hyphae keep to the cell- 



* De Bary observed the same in the case of Peziza sclerotiorum {op. cit., pp. 399 

 — 403), and it is a common phenomenon in fungi. See, e.g., Zopf (Schenk's 

 ' Handb.,' vol. 4, 1889, p. 454). 



f See de Vries," Plasmolytische Studien iiber die Wand der Vacuolen " ('Prings- 

 heim, Jahrb.,' vol. 16, 1885, pp. 565—6). 



% Not impossibly, different zymases are concerned. See Wortmann (' Zeitsch. 

 fur Physiol. Chemi6,' vol. 6, 1882, pp. 287—329, especially pp. 321—329). 



