154 Diseases of Truck Crops 



tacking beet and tomato plants, although complete 

 proof is still wanting. 



The Organism. The cause of pox was first thought 

 to be the fungus Acrocystis batatas E. and H. In- 

 vestigations of the writer showed that this was not 

 the case. Finally Elliot I found that pox was caused 

 by a slime mold organism which he named Cysto- 

 spora batatas E. 



The swarm spores of the slime mold are very 

 small, round, but slightly pointed at both ends. 

 They often fuse in pairs, forming spherical bodies 

 with a single nucleus. The amoebae soon become 

 circular, and four central nuclei together with a dis- 

 tinct wall membrane become apparent. Nuclear 

 division takes place and many nuclei are now formed 

 within the cyst body. As the cyst advances in age, 

 a cell wall is laid down, and each nucleus with its 

 surrounding protoplasm now begins to round up into 

 individual spores. The latter when mature break 

 through the wall of the cyst, which dissolves ap- 

 parently through the secretion of an enzyme within 

 (fig. 25 d). 



It is very doubtful if the organism is carried with 

 infected sweet potatoes, since the spots nearly always 

 dry and fall out. The organism is carried over in 

 the land from year to year. The exact means by 

 which it is carried from place to place is not definitely 

 known. The organism does not seem to spread very 

 rapidly to adjoining neighboring fields, nor to places 

 on the same farm. 



1 Elliot, J. A., Delaware Agr. Expt. Sta. Bui. 114 : 3-25, 1916. 



