338 



Cherry Leaf Scorch. 



[SEPT., 



to the new leaves. In Fig. Ill we see at the base of the 

 flowering shoot a number of old dead leaves ; each of these 

 leaves, it must be noted, bears mature fruit-conceptacles of 

 the fungus, from which ripe spores are being ejected. Above 

 the flowers we see the young leaves unfolding. When we 

 remember that each dead diseased leaf bears many hundreds of 

 fruit-conceptacles, and that each concept acle contains a large 

 number (50 to 100 or more) of sacs, each with eight spores, it is 

 easy to understand how the reinfection of the leaves of a tree 

 takes place regularly year after year, unless preventive steps 

 are taken. 



When one of the spores reaches the surface of a young leaf 

 it germinates at once and, piercing the epidermis, gives rise 

 within the leaf to a vegetative spawn {mycelium). This spawn 

 spreads among the leaf-cells, and feeds on them. Large yellow 

 flecks are soon formed in the attacked leaf, and on these spots 

 small conceptacles, filled with minute, long, curved spores, 

 are developed during the summer. This is known as the 

 Septoria stage of the disease. After some months the yellow 

 patches turn brown, and eventually the whole leaf dies, curling 

 up and presenting a scorched appearance. Previous to this 

 the spawn of the fungus has invaded also the cells of the leaf- 

 stalk, penetrating right down to the branch on which the leaf 

 is borne. Now, in the case of a healthy leaf, it is the cells at 

 the base of the leaf-stalk which play the chief part in the 

 process of the detachment of the leaf in the autumn. It is in 

 consequence of the growth of the fungus down the leaf-stalk, 

 and the injury it inflicts there, that the normal process of 

 defoliation is • made impossible in trees afflicted with cherry 

 leaf scorch, with the result that the diseased leaf remains firmly 

 attached to the branch until it rots away in the course of the 

 following summer. 



The cherry itself is often attacked, when it either soon 

 falls off or becomes more or less distorted, and develops hard 

 spots in the flesh. 



Trees which have suffered from the disease for a number 

 of years show a weak growth of wood, due to the leaves infested 

 by the fungus having been turned to a sickly yellow colour, 

 and so prevented from carrying out during the summer months 

 their normal functions in assisting the growth and ripening. 



