486 FOMES APPLANATUS (PERS.) WALLR. IN' SOUTH AFRICA. 



whicli liave died there have been killed by Pomes austmlis. The progress 

 of the disease is apparentl.v very slow, and it must have been at work on 

 these trees for many years. 



\'on Schrenk and Spaulding/'' referring to the disease in 

 cotton-wood caused by Fomes applanatiis, write: 



The writers have repeatedly observed this form of decay in the cotton, 

 but in their experience it usually starts near the base of the trunk in large 

 wounds caused by hre or otherwise. On that account they are not inclined 

 to call this decay of the cottonwood a disease in the sense in which the 

 decays induced by Fomes iii<:iiianus. P. fraxinnphilus, and others, are 

 diseases. There are a large number of species of fungi which, like Panics 

 applanaUis, grow on dead wood, and whicli may now and then grow on 

 living trees. All of these, including Pomes applaiwtus, can grow just as 

 well, and apparently better, on wood after it has been cut from living trees, 

 and should, in the f)pinion of the writers, be considered as saprophytic 

 forms. 



The alx>ve view is rather to the extreme, and even if it 

 holds for the cotton-wood disease in America, it certainly does 

 not for Ijlack ironwood in South Africa, whicli latter is more 

 in agreement with the observation on Acacia dccitrrcus (the 

 wattle) by Petch in Ceylon. W'e must bear in mind that there 

 is no sharp line of demarcation between parasitic and sapro- 

 phytic fungi. As an extreme case of parasitism, we may take 

 the fungus Fomes rlmosus B'erk., which grows only on living 

 trees, and when it has killed its host ceases itself to grow. As 

 extreme cases af saprophytism, we have the fungi which live 

 and grow only on dead organic plant and animal remain? 

 Between these two extremes we have : ( i ) Fungi which start 

 life as ])arasites, and continue to grow and thrive on their dead 

 hosts — they become saprophytic; (2) fungi which start life as 

 saprophytes — e.g., in a wound, etc. — and then grow into the 

 healthy tissue of their hosts, which may ultimately succumb. 



It is in this latter category that we must place Fames appla- 

 natiis. which, even if it does start as a saprophyte, is nevertheless 

 capable of invading living tissues of its host, and is frequently 

 the main cause of the death of trees which it has attacked. 

 Having killed its host, it continues to grow and thrive on the 

 dead remains — it returns once again to a saprophytic life. 



The cycle of this fungus is from saprophyte to parasite and 

 back again to saprophyte, though the parasitic stage is not 

 necessarily essential to the life of the fungus, and is often 

 omitted. Fomes applanatiis. in other words, is a facultative 

 parasi'te. 



Hosts of Fomes applanatiis tx South Africa. 



This fungus has been found on a large number of different 

 trees in Sotith Africa, as the following list indicates. In some 

 instances the host was dead at the time the fructifications 

 appeared, whereas in others the host was still alive : Olea foveo- 

 lata (bastard ironwood) ; on dead and also at the base of live 



* Schrenk Hermann von. and P. Spaulding, " Diseases of Deciduous 

 Forest Trees," U.S.A. Dep. Agric, iUireau of Plant Tndustrv. Bull. 149, 

 p. 5S. 



