1781 



The Classification of Lower Organisms 



the walls containing no cellulose; these releasing naked infective colls with paired 

 unequal simple flagella. 



This inconsiderable group was made known by the discovery of Plasmodiophora 

 Brassicae, the agent of the clubroot disease of cabbage, by Woronin (1878). The 

 proper place of the group in classification has been a puzzle; some students treat it 

 as a class of myxomycetes, others as an order of chytrids. The known characters — 

 paired unequal simple flagella; cells naked in the vegetative condition; and non-pro- 

 duction of cellulose — assure us that this group has nothing to do with proper chytrids, 

 nor with Oomycetes of chytrid body type. The traditional association with myxomy- 

 cetes is tenable. Alternatively, the group would not be out of place next to order 

 Rhizoflagellata (anyone who chooses to put it there should take note that the class 

 name Phytomyxini is older than Zoomastigoda). 



The Plasmodium causes often much hypertrophy of the host tissue. In some forms 

 the mature plasmodium becomes walled; the protoplast undergoes cleavage into uni- 

 nucleate portions; these become swimming cells and are released through a discharge 

 tube. These forms are of much the appearance of Lagenidialea. In the majority of 

 the group the naked plasmodium undergoes cleavage; the resulting protoplasts be- 

 come walled; the resulting spores or cysts, released by decay of the host, discharge 

 their contents as one or two swimming cells. Ledingham ( 1939) and Sparrow ( 1947) 

 report both types of development as occurring in Polyniyxa. Karling (1944) found 

 the walls to contain no cellulose. Ellison (1945) found the flagella to be simple. 



iKyuiU/Tnui wuium/^iiiMiivnirm- 





Fig. 34. — Ceratiomyxa jruticulosa. a. Fruits x 5. b-q, reproductive processes 

 after Gilbert (1935); b, young spores on the surfaces of the fruit; c, d, the same 

 raised on stalks; e^ f, heterotypic division; g, homeotypic division; h, the mature spore 

 ou its stalk; i-n, germination and subsequent processes: the amoeboid protoplast 

 passes through a "thread stage" before rounding up and dividing into four and then 

 into eight; o, production of flagcllum; p, "zoospore" (gamete); q, gametes fusing to 

 initiate the plasmodium. All x 1,000 except Fig. a. 



