447 



May 27. 1918 Pox of Sweet Potato 



musty gray on Krainsky's Ca-Malate agar; thin cream colored growth, surface becom- 

 ing with an ash-gray aerial mycelium, on Czapek's solution aga;r, in which glucose or 

 glycerine took the place of sucrose, the growth is heavy, yellowish, aerial mycelium 

 abundant, gray (glucose) or (white). No soluble pigment is produced on any of the 

 media studied. On potato plug the growth is light brown, no aerial mycelium is 

 produced, plug is not colored. Milk, at 37° C. is hydrolized in 15 days. Gelatine, at 

 15° C. is slowly liquified (10 mm. on 20 days), with no color production in the liquefied 

 portion; the growth is light brown, with no aerial mycelium. On glucose broth a 

 fiocculent uncharacteristic growth is produced. The organism grows very readily 

 on all the media at 37° C. 



Microscopically the following points are to be noted: Spirals are not produced; 

 the aerial mycelium soon breaks up into short cylindrical spores, although many 

 spherical spores are found. 



Actinomyces poolensis is a superficial wound parasite, usually found 

 following the pox spots produced by Cystospora batatas. The former 

 organism will not grow on healthy tubers of the Irish potato. Structu- 

 rally A. poolensis and A. chromogenus differ very little. They can be 

 distinguished only pathologically and when grown parallel on different 

 media. 



THE GENUS ACROCYSTIS NOT VALID 



In descr^omg pox (soilrot) Halsted (5) has figured a new fungus of a 

 new genus and species which he named "Acrocystis batatas E. and Hals." 

 The latter was practically the only described species of the genus Acro- 

 cystis. However, Halsted's drawings of Acrocystis are really mistaken 

 figures for Cystospara batata, a myxomycete, and not a fungus. Elliott 

 (4) and the writer have proved that pox of the sweet potato is caused 

 by a myxomycete, Cystospora batata Elliott. It is therefore evident 

 that Acrocystis batatas does not exist at all, and that the genus 

 Acrocystis is not valid. 



METHODS OF CONTROL 



A careful search through the literature seems to show that Halsted 

 (6, 7) was practically the first to carry out extensive field work on the 

 control of pox. He found that time has a great tendency to increase the 

 spread of pox and at the same time materially to decrease the yield. 

 On the other hand, he discovered that a broadcast application of 300 

 or 400 pounds of both sulphur and kainit per acre would decrease the 

 disease and also increase the yield of marketable potatoes. The experi- 

 ments as carried out by Halsted (<5, 7) are now being duplicated by the 

 writer in the greenhouse, where conditions are more under control. 

 The work, however, has not progressed far enough to justify any positive 

 statements at this time. From a practical point of view the writer 

 decided to ascertain whether an alkaline or an acid fertilizer would favor 

 or control pox in the field. Accordingly an infested field that had been 

 chosen received normal application of i ,000 pounds per acre of a potash 

 phosphate with the following guaranteed analysis : Ammonia 6 to 8 per 



