ANTHRACNOSE OF CUCURBITS. 49 



the open, exposure to sunlight might kill a negligible percentage of 

 the spores. There remains only the factor of actual desiccation, 

 which must be endured by every spore. The spores are, however, 

 quite resistant to desiccation, and as to their longevity while in this 

 state more will be said presently. The subsequent processes of re- 

 washing, floating out the light seed, redrying, and fanning to remove 

 skin fragments are not such as to eliminate contamination. 



Furthermore, not all of the fragments of fruit epidermis and pulp 

 are removed. A considerable percentage of the Ohio seed bore such 

 adhering fragments, and it is quite possible that infectious matter 

 may remain on the seed in the shape of mycelium within these frag- 

 ments. In a small sample of unfanned seed from the seed field 

 observed in October, 1917, numerous fragments of fruit epidermis 

 dotted with blackened acervuli of this fungus were found both free and 

 adherent to seed. In an attempt to prove the viability of the spores 

 on these acervuli and of the mycelium within the tissue by plate tests 

 on December 20 success was not obtained. 



In the watermelon-seed regions some of the growers operate ma- 

 chines, but by the majority the work of seed extraction is done by 

 hand. The fruits are cut in two and the seed and pulp scooped out 

 by hand into tubs, where the mass is allowed to ferment. Then the 

 seed is washed and dried. During this operation infectious material 

 from surface lesions may readily gain access to the seed. 



The process of seed extraction among cucumbers and melons 

 therefore affords ample opportunity for seed contamination with 

 infectious material, and no step in the whole process precludes the 

 possibility of the latter remaining viable and going into storage 

 with the seed. 



FACTORS INFLUENCING EXTERNAL SEED CARRIAGE OF THE FUNGUS. 



There still remains the long period of desiccation upon the seed 

 surface to be reckoned with. Much of the melon seed used is 2 

 or more years old, and this fact offers a real difficult}^. But much 

 of the cucumber seed, for pickles at least, is used the next season 

 and is in storage only seven to eight months. In this regard it 

 should be recorded that spores on leaf lesions in dried specimens 

 have commonly been found viable seven months after the collection 

 of the material. Many spores should therefore remain viable on 

 the seed until the next season, and were appressoria present the 

 resistance to desiccation might be still greater. 



It is also important in this connection to understand the nature of 

 the seed surface. The familiar gelatinous capsule of freshly ex- 

 tracted cucumber seeds is the epidermis of the seed and consists of 

 a single palisade layer of extremely elongated columnar cells pris- 

 matic in cross section and 160 to 260 m or more in height (1, p. 283- 



