Brooks : The Fruit Spot of apples 449 



was passed through a Chamberland filter and its effects upon apple 

 tissue tested, but with only negative results. 



The toxic effect of malic acid and tannin on the fungus was 

 tested in Van Tieghem cells. Germination was entirely inhibited 

 by a .5 normal solution of malic and greatly retarded by .125 ;/ 

 solution. The fungus made a fair growth in the latter solution. 

 With tannic acid, germination was inhibited by a .025 // solution 

 and only an abnormal growth was made in .0125 n solution. 

 The fungus gave a fair growth in .00625 n solution. 



According to Alwood and Davidson (24), Baldwins have .039 

 gram of tannin and .68 gram of acid as malic to each 100 grams 

 of juice from the ripe fruit, i. e., the juice would be about .002 n 

 solution of tannin and about a .1 // solution of malic acid. These 

 data agree with the fact that the fungus makes a fair growth on 

 ripe apples. They show that any large increase in the acidity of 



apple would prevent the development of the fungus in a cider 

 culture. The tannin in the surface zone of the apple is probably 

 greater than the above data would indicate, as tests made by the 

 writer as well as the work of Zschokke (6) show that the tannin 

 content in the hypodermal parenchyma is much greater than in 

 *e more deeply seated tissue. It is interesting to note in con- 

 nection with the extreme sensitiveness of the fruit spot fungus to 

 tannin ^at Alwood and Davidson (24) found the Baldwin apple to 

 be extr emely low in tannin content. 



the 



The relation of the fungus to the host 



In connection with the other work upon the disease a micro- 

 scopic study was made of the fungus as found in the tissue of the 

 s P°ts. In the preparation of material several killing agents were 

 USed ' among these were absolute alcohol, various strengths of 

 chrome-acetic, weak Flemming, Carnoy's fluid, and picro-acetic. 

 the last two were found to be far the most satisfactory. 

 Th eir superiority lay in the fact that they did not cause the 

 j-Nermal and closely related cells to become so hard and 

 " ttle as the others did. Various contrast stains were tried on 

 tissue but none found more satisfactory than Delafield's 

 hematoxylin followed by erythrosin. Both the apple tissue 

 and the older threads of the funeus held the haematoxylin 



