May J7, 1918 Pox of Swcet Potato 445 



MORPHOI.OGY AND LIFE HISTORY OF THE ORGANISM 



The gross morphology of Cystospora batata has already been indicated 

 by Elliott (4). The organism must undoubtedly hibernate in the soil as 

 cysts. This stage probably enables it to resist drouth and cold. Careful 

 experiments by the writer have shown that freezing will not aflfect C. 

 batata in infected soil. Pox-sick soil in flowerpots exposed to outdoor 

 freezing weather during the entire winter will not show the least 

 weakening in the virulency of the causal organism. Similarly, ordinary 

 drying for 12 months will have no injurious effect on C. batata in the 

 infected soil. 



The cysts are heavy-walled, and each individual may contain large 

 numbers of swarm spores or amebae. When the latter are ready to 

 emerge, the cyst wall becomes thinner, until finally the swarm spores 

 break through. Infection of the host may take place by the penetration 

 of individual amebae into the epidermal host cells. This is especially 

 the case with root tips. Ordinarily, however, infection is by means of 

 a Plasmodium or of both methods. The swarm spores are round, but 

 slightly tapered at both ends, and possess a single, short flagellum. 

 Occasionally the swarm spores fuse in pairs, but from the writer's obser- 

 vations this has not been the rule. They are usually active after emerg- 

 ence from the mother cyst. The period of activity, although varying 

 from I to 7 days, is usually short, often less than 30 minutes. They 

 gradually increase in size, taking on the ameboid, then the plasmodial 

 form. At this stage a large number of nuclei are formed by mitotic 

 division. Nuclear division seems to proceed by a definite mathematical 

 ratio of I, 2, 4, 8, etc. Single plasmodia may often contain from 200 

 to 300 nuclei. At this stage and before escaping, the plasmodium be- 

 comes more dense, and thickly granular in the center, surrounded by a 

 clearer zone w hich later becomes a thick cell of the cyst. The latter 

 apparently undergoes a short period of rest, during which time the swarm 

 spores are formed. These in turn emerge and undergo the same life cycle 

 as above described. Thus, in a single infected root tip or in a pox spot, 

 several crops of swarm spores may be formed wthin the host cells, each 

 generation of which advances farther. Finally all the plasmodia seem to 

 collect, cease advancing, turn backwards, and leave the pit for the soil. 

 It is probable that the plasmodia in the soil encyst and pass the winter 

 in that way. Numerous cytological and morphological studies of this 

 important organism are still in progress. 



A NEW SPECIES OF ACTINOMYCES ASSOCIATED WITH POX 



Of the many bacteria and fungi isolated from pox, a species of Actino- 

 myces is very often obtained from diseased spots. Because of the per- 

 sistence of this organism, work was undertaken on it by the writer. 

 Inoculation experiments with pure cultures of this organism showed that 



