34 MYCETOZOA AND RELATED ORGANISMS 



report. Webb (1949) reports the occurrence of sporangia of this fungus in 

 root hairs of Rumex sp. and Holcus lanatus L., growing in infested soil. 

 These roots were carefully washed and planted in sterile soil. Seedlings of 

 Brussels sprouts (Brassica sp.) planted in the pots along with these washed 

 roots developed the disease. In spite of numerous extended studies on this 

 parasite, many contradictory reports have been published. Thus P. M 

 Jones (1928) reports eight swarm spores emerging from the resting spore 

 and their fusion by twos so that infection of the root hairs is by means of 

 amoeboid zygotes. Fedorintschik believes that the nuclei of the zoospor- 

 angia formed in the root hairs are diploid and that two meiotic divisions of 

 the nucleus occur as the swarm cells are formed, these last fusing by twos, 

 as reported by Cook and Schwartz. Karling (1942) doubts the sexual 

 nature of these swarm cells and suggests that they are only secondary 

 zoospores, such as are reported in some other so-called Plasmodiophorales. 

 Several other species have been ascribed to the genus Plasmodiophora but 

 their life histories have not been studied and it is not at all certain that 

 they belong here. (Figs. 7, 8.) 



The other genera which Karling admits to this order, which has but 

 one family, are as follows: 



Tetramyxa: causing pronounced hypertrophy of host tissues, developing spores 

 in twos or fours, and with sporangia and sexual stage unknown, and 

 zoospores not seen. 

 Two or possibly three species in stems or roots of seed-plants. 



Odomyxa: spores usually develop in eights, sporangia numerous, zoospores 

 anteriorly biflagellate, one flagellum directed forward, a longer one pos- 

 teriorly, when swimming. No sexual stage known. Cell walls not of cellu- 

 lose. Causes gall-like enlargements in Achlya glomerata Coker. 



Sorosphaera: spores compacted into a hollow sphere, zoosporangia are formed 

 (Ledingham, 1939) and their zoospores anteriorly biflagellate and hetero- 

 cont. Spore walls do not contain cellulose. 

 Two species: S. veronicae Schroeter forms galls in the stems of Veronica; 

 S. radicalis Cook & Schwartz forms galls in the roots of grasses. In the 

 former zoosporangia are unknown, in the latter thin-walled zoosporangia 

 are formed. Sexual reproduction not demonstrated. 



Sorodiscus: spores formed in a disk-shaped sorus usually in two layers, much 

 like a flattened spherical sorus of Sorosphaera. Zoosporangia and character 

 and number of flagella unknown. Sexual reproduction not observed. 

 Two species : one in stems of Callitriche and one in Chara. 



Spongospora: spores in a hollow sphere with several openings, zoosporangia are 

 formed according to L(Mli,igham (1935), zoospores anteriorly biflagellate 

 and heterocont, similai' in size whether from sporangia or from resting 

 spores. Sexual fusion of myxamoebae reported by Cook (1933). 

 Best known species is S. subtcrranea (Wall.) Lagerheim causing the powdery 

 scab of the tubers of potato {Solanum tuberosum L.). It also attacks the 

 stems and roots of this host and of related plants. 



Ligniera: spores in irregular clusters, usually not causing hypertrophy of 

 tissues except of root hairs in one species. This, according to Palm and 



