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1920] WILLAMAN—SCLEROTIXIA 227 



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pectin coagulum. The lower layer merges into the loose coagulum 

 of the medium, and most of it easily sloughs off when the felt is 

 washed in water. When an apple juice rather high in pectin is 

 used, the whole mass becomes a rather soft gel within a few days. 

 This gel enables the fungus to build up a semi-solid medium upon 

 which to support aerial hyphae and sporophores. 



The possible function of pectase to the fungus when invading 

 a host tissue offers a subject for speculation, at least. The sub- 

 stance of the middle lamella is usually spoken of as calcium pectate. 

 That it is the same substance as the calcium pectate gel formed by 

 pectase is rather doubtful (2, 5). The work of various investi- 

 gators has proved conclusively that this fungus dissolves out the 

 middle lamella, either by the enzyme pectosinase or by oxalic 

 acid. If it be oxalic acid, the calcium of the middle lamella would 

 be removed as insoluble calcium oxalate, leaving a pectin residue, 

 presumably soluble, or at least no longer capable of cementing the 

 cell together. Whether Sclerotinia has the power of forming a 

 calcium pectate gel out of such pectic residue is not known, since 

 the nature of this material is not determined. If, however, the 

 solution of the middle lamella be brought about by pectosinase, 

 we have a different case to consider. We really know nothing 

 definite concerning the action of this enzyme on the middle lamella, 

 but presumably some simpler pectic substance would be formed 

 along with a soluble calcium complex. The fungus would pene- 

 trate the dissolved substance of the lamella, and then reprecipitate 

 it, presumably as the calcium pectate found in the apple juice 

 cultures. Since it is not known whether the pectin obtained by 

 boiling a ripe fruit in water is the same as the pectin produced by 

 the action of pectosinase on the middle lamella, we are perhaps 

 not entirely justified in assuming that the same substance is 

 formed by pectase acting on dissolved middle lamella in vivo and 

 on soluble pectin in an extracted fruit juice. The work of previ- ' 

 ous investigators, however, gives us good reason to believe that 

 the pectic gels in the two cases are very similar, if not identical 



(2, 5, 10). 



Given this hydrophyllic gel, what purpose may it serve the 



invading parasite ? Valleau believes that the reason Sclerotinia 



