Immunity in Multicellular Plants 33 



petunias, dahlias, etc. The mycelium of this Sderotinia develops in 

 the stems of herbaceous plants and produces sclerotia inside them, 

 forms of resistance, which in this instance are black and resemble 

 small particles of mouse excrement. 



The spores of the Sderotinia germinate and form mycelial threads 

 [on the surface of the plants. In order that they may penetrate into 

 the tissues these threads must attack the cell-membrane and for this 

 purpose they secrete a fluid, which contains both a digestive ferment 

 nd oxalic acid, the latter being essential for the action of the ferment 

 The presence of this " toxin " has been demonstrated by de Bary 

 y macerating the mycelium of the Sderotinia. The resultant extract 

 las a well-marked action on the tissues of many plants (carrot, 

 erusalem artichoke, chicory, etc.). Under its influence the proto- 

 ilasm of the cells contracts, a genuine plasmolysis is set up, the cell- 

 embrane swells and its layers between the cells are dissolved. As 

 he result of this digestive action, the cells become separated and 

 he tissue softens. This extract, when heated to 52 C., loses its 

 igestive action on the cellulose membrane, but still retains its power 

 if setting up plasmolysis. This reaction to temperature confirms the 

 iew that the juice of the Fungus contains a soluble ferment. The 

 suits of de Bary's researches have been confirmed and in part 

 Lipplemented by the experiments of Laurent 1 . 



It is a fact of common observation that the Sderotinia libertiana 

 vades for the most part young plants. It may therefore be asserted 

 hat the disease produced by this Fungus is, like scarlatina or measles 

 the human subject, an "infantile" disease. De Bary suggested 

 hat the immunity of adult plants must depend on the greater 

 sistance which their cell-membranes offer to the fluid secreted by 

 |he mycelial filaments. Direct experiments have shown the accuracy 

 f his suggestion. Whilst the fluid extracted from the Sderotinia 



ily digests the tissue of young plants it leaves intact that of adult [36] 

 ilants of the same species. 



In the course of this disease we have a struggle going on between 

 plants. The parasite brings into play toxic and digestive secre- 

 ions with which it seeks to impregnate its host. The attacked plant 

 efends itself by the secretion of membranes capable of resisting the 

 :tion of the secretions of the Fungus. This struggle by means of 

 liemical substances is, however, directed by the activity of the living 



1 Ann. de VInst. Pasteur, Paris, 1899, t. xm, p. 44. 

 B. Q 



