THE SARCODINA 243 



SUBORDER II. : SOEOPHOBA (Acrasiae, Pscudoplasmodida). With no 

 flagellate stage in the life-history ; the amcebulae do not fuse completely to 

 form a true plasmodium ; the spores are formed in clusters (" sori "). Here 

 belong various genera, for the most part found in dung, such as Dictyostdium 

 and Copromyxa. Acrasis occurs in beer-yeast. 



In addition to the typical Mycetozoa belonging to these two suborders, 

 there are a number of forms on the border-line, referred by some authorities 

 to the Mycetozoa, by others to other orders, such as the Proteomyxa. It 

 is only possible to refer very briefly to these genera here. 



In the first place, there are a number of parasitic forms, placed together 

 by DoHein in the suborder Phytomyxinoe, Schroter. In this suborder no 

 sporangium is formed, the process of spore-formation being simplified, 

 probably, in correlation with the parasitic mode of life. The typical members 

 of this group are parasites of plants, but some recently-described parasites 

 of insects have been assigned to Phytomyxinoe. The best known example of 

 the group is the common Plasmodiophora brassicce, which attacks the roots 

 of cabbages and other Cruciferae, producing a disease known as " Fingers 

 and Toes " (" Kohlhernie "), characterized by knotty swellings on the roots. 

 Other genera parasitic on plants are Tetramyxa and Sorosphcera. 



In Plasmodiophora the spores germinate to produce flagellulae, which are 

 liberated in water or damp earth, and which in some way penetrate into the 

 cells of the plant, and there appear as the myxamoebae after loss of the flagel- 

 lum. The youngest myxamoebae seen have two nuclei. They grow in the 

 cell-contents with multiplication of their nuclei, and fuse with one another 

 to form plasmodial masses which fill the cell after absorption of its contents, 



In a diseased plant a number of cells are attacked by the parasite, and it is 

 not certain whether the myxamcebae can pass from one cell to another, and so 

 spread the infection, or whether all the infected cells are derived from the 

 multiplication of the first cell infected. The second view, maintained by 

 Nawaschin, is supported by Prowazek, and also by Blomfield and Schwartz, 

 with regard to the allied genus Sorosphcera. 



When the host-cell is exhausted, the reproductive phase begins, according 

 to Prowazek (127), by the nuclei of the plasmodium throwing out numerous 

 chromidia, and becoming in consequence very indistinct. In Sorosphcera at 

 this stage (Blomfield and Schwartz) the nuclei disappear altogether, being 

 entirely resolved into chromidia from which secondary nuclei are formed. 

 Spore -formation, preceded by sexual processes, takes place in the manner 

 described above (p. 149, Fig. 76). In Sorosphcera, Blomfield and Schwartz 

 found that, after reconstitution of the generative nuclei, the plasmodium 

 divides up into uninucleate cells, each of which divides twice by karyokinesis ; 

 after these divisions the cells become arranged as a hollow sphere, the " soro- 

 sphere," and each cell becomes a spore. No cell-fusions or syngamic processes 

 were observed. 



As stated above, certain parasites of insects are referred to this order 

 by Leger. Such are the genera Sporomyxa, Leger (295), Mycetosporidium, 

 Leger and Hesse, and Pdtomyces, Leger (C.R.A.S., cxlix., p. 239). Zoomyxa 

 legeri, Elmassian (637), parasite of the tench, is perhaps also to be referred 

 to the Mycetozoa. The position of these forms must, however, be considered 

 somewhat doubtful at present. Chatton has thrown out the suggestion 

 that the affinities of Pdtomyces are rather with the Cnidosporidia (p. 409), 

 through the genus Paramyxo recently found by him (761). 



Lastly, mention must bo made of the remarkable genera Chlamydomyxa, 

 Archer, and Labyrinthula, Cienkowski, the affinities of which are still obscure. 

 By Lankester (11) they were ranked as an independent order of the Sarcodina 

 under the name Labyrinthulidea ; by Delage and Herouard (6) and others 

 they are placed as a suborder, Filoplasmodida, of the Mycetozoa. 



Chlamydomyxa is a fresh-water genus occurring either free or encysted. 

 Its most remarkable feature is the possession of chromatophores which enable 

 it to live in a holophytic manner, and consequently to assimilate and grow 

 when encysted. On the other hand, when free it forms a network of long, 



