1904.] 



Origin of Parasitism in Fungi. 



i53 



gain an entrance. As a general rule it was found that if a weak 

 solution of sugar was introduced beneath the skin of the leaf, 

 and if the spores of our commoner parasitic fungi were dis- 

 tributed on the patch so treated, the fungus had the power of 

 entering and living on the sugary solution, and eventually of 

 attacking adjoining tissues. If, on the other hand, a weak 

 solution of acids was introduced, the fungus as a rule showed 

 no disposition to enter. Certain fungi are purely saprophytic, 

 that is to say, can only live on dead vegetable matter ; and yet 

 by gradually accustoming them to push their tubes into living 

 plants by injecting a substance by which the fungus is attracted, 

 Mr. Massee has been able to " educate " such fungi into becoming 

 parasites, that is to say, fungi capable of attacking living plants. 

 He comes to the conclusion that all parasites have developed 

 from saprophytes, and that it is quite possible for a harmless 

 fungus living on dead vegetable matter to acquire the habit of 

 living on growing plants. As a case in point he cites the fungus 

 Dendryphium comosum, which, until recently, appears to have 

 been quite unable to attack living plants, but which, aided by the 

 unnatural conditions under which certain glass-house crops are 

 now grown, has been found to attack in a serious manner young 

 cucumbers. 



Although the subject of inducing saprophytes to become 

 parasites is one that has but little interest for the practical 

 farmer or gardener, the case is different where the problem is 

 attacked by the botanist from the other side, Reference has 

 already been made to the result of " educating " turnips and 

 wheat to resist certain diseases, and we also know that certain 

 varieties of potato are much more resistant to the attack of the 

 parasite that produces potato disease than others ; in fact, 

 immunity to disease is a matter constantly in the minds of the 

 raisers of new kinds of potatoes. 



Doubtless there is a great field open to scientific work in this 

 direction, and it is a subject that interests the forester as well as 

 the farmer and gardener. Although the task of producing a 

 tree which shall prove resistant to the attack of some disease 

 must proceed much more slowly than in the case of an 

 annual or herbaceous plant, still it seems not to be beyond 

 the bounds of possibility that one day we may find our- 



