346 



of a fungus may live as a parasite, while that producing the asci- 

 gerous fruit lives as a saprophyte on dead and often fallen por- 

 tions of the same plant. In countries with a very marked change 

 of climate in summer and winter this power may be of consider- 

 able economic value, since the saprophytic stage may serve to 

 carry the fungus through the winter and give rise to new out- 

 breaks of disease in the succeeding spring. In mild winters the 

 parasitic stage may persist, but under extreme conditions the 

 saprophytic form may alone be able to survive. An investigation 

 of this problem is of more importance in temperate countries than 

 in the more uniform climatic conditions of the tropics, yet even 

 there it 'should hardly be entirely neglected. It is possible, for 

 example, that definite knowledge of the part played in spreading 

 infection by the ascospores of Roscllinia bunodcs, the black root 

 disease fungus, would be of value. The perithecia in this instance 

 always develop on a saprophytic mycelium, some time after the 

 tree is dead. Their growth is slow and the spores have a thick 

 outer coat — all facts which point to this stage as intended to carry 

 the fungus through unfavorable conditions. It would appear, 

 however, that most fungi perpetuate themselves in the tropics 

 largely by means of conidia, since the ascigerous stage is often 

 either entirely absent or only rarely formed. 



The question of the conditions under which some saprophytic 

 species of fungi become parasites is one of very great importance 

 in the tropics, and one on which some information, of a rather 

 preliminary nature, has been obtained. Quite a large number of 

 the more serious diseases of crops are caused by fungi that are 

 far more usually saprophytic than parasitic in habit. As an ex- 

 ample may be taken the ubiquitous lliyridaria tarda found as a 

 saprophyte on an immense number of different plants, and as a 

 wound parasite on cacao, Hevea and tea, among other hosts. Its 

 parasitism is largely dependent on conditions unfavorable to the 

 growth of the host, as well as on other factors. Again, the root 

 disease of Para rubber in the East is due to a fungus (Fames 

 scniitostus) usually sapro])hytic on forest stum])s. Its ])arasitism 

 depends on the presence of large quantities of decaying wood 

 which afford it food for vigorous vegetative development before 

 it begins its attack, and on the presence of an ample supply of 

 moisture. The same is probably true to some extent of Rosclli)iia 

 biDiodcs referred to above, 'llie solulit)n of the problem in con- 

 nection with many species of the family of bracket fungi ( Poly- 

 poraceae I, to which Pomes scmifostiis l)elongs, is a matter of some 

 importance in the tropics, as many of them ajipcar to act occa- 

 sionally as wound parasites or as root ])arasites on trees ])lanted 

 in newly cleared forest land. Similar investigations would be 

 valuable in the case of many of the toadstools ( Agaricaceae) and 

 of the genera Colletotrichum and Gloeosporium. of which many 

 forms are found on ripe or fallen fruits. 



Of the last of Professor Salmon's cjuestions, namely, what are 



