228 BOTAXICAL GAZETTE [September 



produces a firm and not a soft rot of plums is that its comparatively 

 large hyphae completely fill the intercellular spaces produced by 

 the collapse of the cells, and that thus the tissue retains its shape 

 and firmness, even after rotting. The writer believes it much more 

 probable that the laying down of considerable calcium pectate gel 

 maintains the firmness of the rotted tissue. This view is further 

 supported by the evidence already stated that this fungus does not 

 consume pectic material in its metabolism to any marked degree. 

 Certain advantages to the fungus can be seen in this production 

 of calcium pectate gel. Since a fruit, rotted on the tree by this 

 fungus, typically retains its form and turgidity for some time, the 

 fungus is enabled to sporulate (chlamydospores in this case) 

 copiously for several days, during a period when the tree is 

 full of ripe fruit susceptible to the rot. Again, many of these 

 rotted fruits do not drop from the tree; they slowly shrivel up, 

 usually without any break in the skin, and form the characteristic 

 mummies of plum and peach orchards. The following spring 

 these mummies imbibe water readily, due in great part to the 

 strongly hydrophyllic calcium pectate gel, and again sporulate 

 profusely. After this the mummies drop to the ground and remain 

 dormant for a year, when they again imbibe water, and produce 

 an abundance of ascospores at the time of blossoming of the fruit 



trees. 



Summary 



Sclerotinia cinerea, when grow r n on a fruit juice containing 

 soluble pectin, coagulates this pectin to a gel of calcium pectate 

 by means of the enzyme pectase. When simple sugars are avail- 

 able, the fungus does not assimilate pectic substances. When, 

 however, pectin alone is available, it is slowly assimilated. The 

 mycelium contains no pectic substances, except such as occur in 

 particles of calcium pectate gel enmeshed by the hyphal filaments. 

 When the fungus invades a tissue, it follows the line of the middle 

 lamella by dissolving out the latter with the enzyme pectosinase. 

 It probably reprecipitates the pectin of the lamella as calcium 

 pectate. The latter, being a hydrophyllic gel, maintains the firm- 

 ness of the fruit even after rotting, which is a characteristic of fruit 

 rotted by Sclerotinia. This highly imbibing gel is probably also 





