AGGRESSIVE PARASITISM OF FUNGI 



BY T. J. BURRILL. PROFESSOR OF HORTICULTURE IX THE ILLINOIS 



INDUSTRIAL UNIVERSITY. 



It louf;' has been and still Cdntinues to be ti disputed question among horti- 

 culturists and botanists, regarding diseases of plants accompanied by fungous 

 growth, as to whether the latter is the cause or the result of the disease. Like 

 other questions, open to protracted debate, there are, undoubtedly, two sides to 

 this one. Cases are not all alike. Sometimes disease and eyen death, attributed 

 to this cause, take place before any evidence of fungi make their appearance, while 

 under other circumstances the reverse may be true. But a greater source of differ- 

 ence of opinion comes from the want of fully understanding the habits and laws of 

 growth in general of both kinds of plants, the afflicted and the afflicting, and 

 in particular the special habits and laws of growth of the individual species 

 concerned. As an illustration from the animal world we may take two snakes 

 that look very much alike, and that, to common observers, would be pro- 

 nounced to be the same, while their bite upon these very observers would pro- 

 duce strikingly different effects. One is harmless, the other deadly poisonous. 

 The illustration, however, does not end here. The poisonous nature of one of 

 the reptiles is proved only so far as experiment has been tried ; for while there 

 is the above difference between them in regard to their effects upon man, their 

 bite may be in no wise different in its effects upon swine. It is even possible 

 that the harmless and poisonous natures may be exchanged in regard to some 

 animals bitten by them. Thus the question becomes a complicated one, and 

 can only be settled by having at command all the facts in the case. Even upon 

 the same animals the effects may not always be the same, for the conditions of 

 the system change in such manner that disease is caused at one time, and at 

 another the influence is entirely thrown off. Now, knowing these and similar 

 things to be true of animals, does it not seem probable that like complications 

 may be found among plants ? If it is admitted that much close observation is 

 necessary in order to arrive at truthful conclusions among beings which are 

 Avell known, and whose actions are easily seen, what must follow as a necessity 

 when we deal with comparatively unknown forms, whose workings are in secret, 

 and of whose mysterious energies we know little or nothing ? Is it a wonder 

 that men should have disagreed about the habits and influences of living 

 structures, too small to be seen at all by the unaided vision, and too subtle in 

 their operations to be discovered except by skillful and laborious research ? 

 Such, however, are the most of the parasitic fungi. Thousands of these minute 

 forms find lodgement upon a single leaf, yet their presence is unsuspected by 



