PREVENTIVE AND COMBATIVE MEASURES. 71 



sites, much may be done to shorten the existence of a disease, 

 and to prevent its reappearance in the following spring. 



Fungi which reach maturity on fallen leaves are easily com- 

 bated in this way. Hartig gives a striking example of the 

 success of this measure. In the English Garden, a large park 

 in Munich, the leaves are carefully removed at frequent intervals 

 as they fall, and utilized as stable-bedding ; here Rhytisma 

 acerinum, the black spot of the sycamore leaf, is hardly known, 

 whereas in the park at Nymphenburg, and in other places 

 round Munich, where the leaves are allowed to remain lying, 

 the leaf-spot is very common. Rhytisma salicinum can be 

 treated in the same way in osier-nurseries. In plum orchards 

 Polystigma rubrum may be held completely in cheek by removal 

 of fallen leaves. So also the numerous mildews (Erysipheae) 

 of our cultivated plants. Cherry leaves killed by Grnomonia 

 erythrostoma remain hanging on the trees, but the disease has 

 almost disappeared since the practice of removing and destroying 

 these was introduced in gardens, like those of the Altenland, 

 once completely devastated by this parasite. 



The progress of the disease caused by Nectria cinndbarina is 

 reduced if the branches which die during the summer be at 

 once removed and burnt before the red fructifying patches 

 appear. It would also be advisable to burn in the autumn 

 other dry brushwood, since it frequently contains Nectria and 

 other wound-fungi, and if left over winter only serves as a 

 nursery and source of infection for all neighbouring trees. In 

 a similar way should be treated branches infected with sporo- 

 carps of Ciuyurbitaria lahurni and such-like fungi. 



Immediate removal, burning, or burying of young trees 

 attacked by Phytophthora omnivora is' of advantage in prevent- 

 ing the distribution of the fungus by conidia and swarm-spores 

 during summer, its hibernation in dead tissues, and its continued 

 distribution in the following spring. The hibernating oospores 

 of many other lower fungi may be similarly got rid of by 

 destruction of the plant-remains inhabited by them. 



II. Removal and destruction of diseased plants or portions of these. 



(1) The removal of symbiotic organs comes here particularly 

 into notice. Amongst these are the " witches' brooms " which 



