FUNGI 7 



fungus alone coming to the surface; and as the production 

 of fruit is the final act in the life of the fungus, it may 

 be accepted that the fungus has done its worst when it 

 produces fruit. 



The above account shows that the argument frequently 

 brought forward, that as the fungus (sporocarp) has only 

 appeared on dying or dead parts, it cannot be the cause of 

 the disease, is not necessarily correct. On the other hand, 

 the presence of a fungus on a diseased portion does not 

 necessarily prove that the fungus was the cause of the dis- 

 ease. This has to be proved or refuted by proper methods. 



An exception to this rule is met with in the group of fungi 

 represented by the hop mildew {Sphaerotheca castagnei^ Lev.), 

 where the mycelium or vegetative portion of the fungus 

 is quite superficial, forming white patches on the surfaces 

 of living leaves ; certain short branches of the mycelium, 

 called haustoria or suckers, pierce the epidermis of the leaf, 

 enter the cells, and absorb the food required by the fungus. 

 The mycelium consists of very slender, thin-walled tubes 

 called hyphae. In the fruit and certain other structures 

 these hyphae are densely interwoven, forming solid parts ; 

 and often the walls of the hyphae are thickened to such an 

 extent that a structure as hard as wood is produced. 



Reproduction of Fungi. — The majority of fungi are 

 short-lived, and the arrangements for reproduction, or the 

 continuation of the species, are usually provided for on a 

 very lavish scale. In this respect again, fungi differ very 

 materially from flowering plants. In the latter there is only 

 one form of fruit produced, the seeds of which reproduce 

 the species; whereas in the great majority of parasitic fungi 

 there are at least two distinct forms of fruit, and in many 

 kinds three or even four distinct and very different-looking 



