FUNGI. INTRODUCTORY 



395 



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El: 



A ferment has been extracted from large cultures of a certain Botrytis, 

 and found to act upon cell-walls, causing them to swell. Such swelling 

 is a feature of the perforation by the 

 invading hypha, which first softens 

 the cell-wall, and then penetrates the 

 softened mass, finally emerging on the 

 other side (Fig. 294, iii.-viii.). This 

 power of perforation has been found 

 in certain cases to depend upon the 

 nutrition of the Fungus : for instance, 

 Sclerotinia sclerotioriun can only pene- 

 trate living tissue after a period of 

 saprophytic nutrition. There is, how- 

 ever, another side to such questions in 

 the case of parasitic attack : viz. the 

 power of resistance of the victim, 

 which depends partly upon the thick- 

 ness of the protective walls, but pro- 

 bably also on the presence or absence 

 of inhibiting substances. Thus fungal 

 attack may be regarded as a balance 

 of physiological powers between the 

 invader and the host. In fact, it 

 stands on a footing similar to that of 

 mycorhiza in Phanerogamic Plants, or of conditions of symbiosis 

 generally (see Chapter XII.). 



KV 



Fig. 293. 



Sclerotium of Ergot of Rye (Claviceps), 

 a mass of pseudo-parenchyma formed in 

 the ovary of Rye : above is the style still 

 covered by remains of " Honey-Dew " 

 (see p. 425, Fig. 325, a). 



Fig. 294. 



Successive stages of the penetration of cell-wall of Lily by the hypha of the 

 Fungus causing the Lily disease. (After Marshall Ward.) 



