EXPERIMENT STATION BULLETINS. 



285 



The greatest injury follows when the fungus shows early in the season 

 upon the fruit, especially if the blossom stems are attacked. They 

 are small and delicate, and a very small fungous spot will serve to 

 girdle and destroy them. The spring of 1892 seemed to promise a large 

 crop of apples, as the trees blossomed full, but heavy and continuous 

 rains occurred while the fruit was in blossom, and not only caused an 

 imperfect fertilization of the flowers and a failure to set, but, the condi- 

 tions being favorable for the development of the apple-scab fungus, most 

 of the others were so badly attacked that they soon dropped, or rotted upon 

 the trees. 



Fig. 4. 



Pig. 4. Section thron^h a ecab spot, a, spore (conidiam) ; 6, hyphaor sapporting thread; c, myceliam, 

 or plant body of f angas ; d, epidermis of apple; e, cells of apple ; /, spores greatly magnified; g, h, 

 eporee germinating. 



When they first appear, the scab spots upon the fruit are about the same 

 as upon the foliage, but, later on, the cells that have been destroyed take 

 on a brownish-white appearance, while a dark-green circle surrounds them 

 in which the fungus is still at work, and from which it constantly extends 

 to the surrounding tissues, checking the growth of the affected parts, and 

 often causing the fruit to crack. During hot, dry summers the fungus 

 seems to rest, but if the season is moist the spread is rapid and the injury 

 is often very great. It is estimated that in some states the loss ranges 

 from one sixth to one fourth of the crop, often reaching a half million 

 dollars. 



Not only is the development of the fruit stopped, if it is not prevented 

 altogether, but the injury to the foliage is so great that the tree can 

 neither develop the fruit it does set, nor form fruit buds for the next 

 year's crop. The microscopical structure of this fungus is shown in 

 Fig. 4. 



In 1889 careful experiments with various fungicides were made and it 

 was demonstrated that, with a comparatively small expense for labor and 

 materials, nearly ninety per cent, of the fruit would he free from scab, 



