1915] 



WESTERDIJK PHYTOPATHOLOGY IN THE TROPICS 



309 



I shall begin the consideration of the different groups of 

 fungi which cause plant diseases in the tropics by mention- 

 ing one biological group of hymenomycetous fungi the mem- 

 bers of which attack tropical cultivated plants. These are 

 the so-called root fungi. It is certain that the root parasites 

 belong to different species of Hymenomycetae, and that one 

 species of host-plant may be attacked by a number of species 

 of these fungi. Several of the latter, if not all, are charac- 

 terized by the peculiar mycelium characteristic of the 

 Hymenomycetae; in many cases, however, fruiting bodies 

 have never been found. Practically all cultural woody plants 

 — tea, coffee, rubber, quinine, cacao, coca — may suffer from the 

 attacks of root-fungi, these attacks occurring mostly on virgin 

 soil. The fungi develop on the decaying stumps of the forests, 

 grow through the soil, and reach the roots and stem bases of 

 the young tea, coffee, or quinine plant. The bark is pene- 

 trated and the mycelium destroys both bark and wood (the 

 mycelium strands can be very clearly seen between bark 

 and wood). Whereas young plants up to three or four years 

 old nearly always are killed, older ones may resist; different 

 species of plants, however, behave differently in this respect. 

 In some districts the fruiting bodies of Fomes semitostus 

 appear on the dying plant or on the dead roots, but in others 

 fruiting bodies have never been found. 



A second biological group of fungi, so common in our lati- 

 tudes, has only a few representatives in the tropics under dis- 

 cussion. I am speaking of those ascogenous or imperfect 

 fungi which cause the die-back diseases of our orchard, forest, 

 and park trees, e.g., Valsa, Diplodia, and others. These fungi 

 kill the branches by penetrating into the bark and sometimes 

 into the wood. They appear on our trees when these are in a 

 dry condition, and in dry climates or in dry years such dis- 

 eases are of importance. Not so, however, in the tropics. 

 The only die-back disease which is common is caused by 

 Corticium javanicum, which, however, belongs to the Hymen- 

 omycetae and forms red layers on twigs, branches, and even 

 trunks of all cultural woody plants, e. g., rubber, coffee, 

 quinine, tea, cacao, coca, and fruit trees. We find the disease 



