PLANTS, FUNGI AND INSECTS 13 



Fungi which attack living plants parasites are, naturally, 

 of more importance to the fruit grower than those which feed 

 on dead tissue saprophytes; but the two classes sometimes 

 merge into each other, and a fungus which is usually a saprophyte 

 may, under altered conditions, become a parasite, and attack 

 living plants. In some cases, also, a parasitic fungus reaches the 

 seeding stage only when on the dead wood of the plant which 

 it has killed. 



Moulds and mildews are commonly differentiated from other 

 fungi by being confined more to the surface of the host plant, 

 their mycelium penetrating only a short distance into the sub- 

 stance of the leaves, shoots, etc. 



For the destruction of fungus spores, the fungicide must be 

 applied either in summer or in winter, according as it is the 

 summer spores or winter spores which have to be attacked. One 

 essential to the successful dealing with the summer spores is to 

 do the spraying on the very first appearance of the disease : in 

 most cases, however, such spraying results only in a checking of 

 the attack, for the mycelium -is not destroyed by it, and a 

 renewed formation of spores occurs later on, necessitating a 

 repetition of the spraying operation. 



Besides spraying the trees in winter for the destruction of the 

 winter spores, it is very important that all dead leaves, shrivelled 

 fruit, and prunings should be collected and burnt, for it is on them 

 that the spores are generally found. All wounds should be 

 attended to and tarred, for in many cases it is through some wound 

 that the fungus spores gain an entry into the tree ; unfortunately 

 they may enter through wounds too minute to be noticed, such 

 as those made by the woolly aphis, and the destruction of pests 

 of that description is, therefore, one of the best ways of keeping 

 the trees free from the attacks of fungi. 



INSECTS 



A knowledge of the life-history of an insect is essential whenever 

 it is a question of destroying it, for there is often only one period 

 in its life when it is vulnerable. Generally speaking, there are 

 four distinct stages in the lives of all insects : (i) the egg, (2) the 

 larva, maggot, grub or caterpillar, (3) the chrysalis, nymph or 

 pupa, and (4) the perfect insect or imago. The true pupal stage 

 is absent in the case of mites and spiders, whilst in that of some 

 insects, such as aphides and leaf-hoppers, there is no pupal stage 

 similar to that existing in the case of a moth, where the pupa is 

 quiescent, and does not feed. 



