5 



area, become more readily and seriously parasitic and will, 

 unless checked, invariably proceed rapidly in the living tissues 

 and occasion much damage. This form of parasitism, in 

 various degrees of intensity, is seen in the following diseases of 

 fruit-trees: Brown-Rots, Die-Back of Plums, Apple Canker 

 and Silver Leaf. Lastly, there are the exclusively parasitic 

 forms of which it may be said, in a general way, that their power 

 to bring about the infection of sound, uninjured tissue is con- 

 fined to the leaf -attacking species, which are found principally 

 in three natural groups, the rusts, the mildews and the false 

 mildews. Alighting on a leaf, the moisture provided by a 

 light dew allows the spores to germinate and the germ tube 

 of the spore rapidly enters the leaf, either through the stomat.a- 

 (or breathing pores) or by piercing its way through the epider- 

 mis or outer skin of the leaf. The true rusts (such as Plum 

 Bust), the false mildews (few of which attack fruit) and the 

 Apple and Pear Scab fungi effect an entrance in this way. 

 The true mildews, such as American Gooseberry Mildew and 

 Apple Mildew, are highly parasitic but differ from other fungi 

 in being superficial and extract all their nourishment by means 

 of minute suckers which penetrate the epidermal cells. The 

 damage that mildews cause, however, is very severe. 



Mode of Attack and Measures of Control. The method 

 of attack, subsequent development and above all the means of 

 hibernation of fungus parasites are, from the practical stand- 

 point, of very great importance and should be mastered by 

 every fruit grower. In the leaflets a short outline is given in 

 each case, but a very brief summary is added below, the dis- 

 eases being grouped according to the nature of the damage 

 caused. An indication of the type of treatment required is 

 also stated. 



(a) Fungi attacking the Leaves. Leaf fungi, though com- 

 prising many forms, are usually combatted by spraying or 

 dusting. Spraying may aim at the prevention of an attack or, 

 more rarely, at the destruction of the mycelium and spores. If 

 the leaves are covered with a film of fungicide, the slender 

 germ tube which the spore produces on germination is killed 

 and infection does not- take place. The action of the spray 

 here is preventive. To mildews, the mycelium of which is 

 superficial, a spray or powder may be applied with the object 

 of the actual killing of the mycelium. This is often largely 

 successful, but, even with mildews a preventive spray is more 

 effective and should always be employed if possible. 



The method of hibernation varies considerably. Where this 

 is known it is often possible almost to exterminate the fungus 

 by the removal of the winter stage. In mildews the normal 

 method of hibernation is by means of resting spores 

 contained in spore-cases produced on the old mildew patches 

 either on the leaves or shoots. The affected leaves and shoots 



