MYXOMYCETES 405 



flows into these processes and finally breaks up into numerous polyhedral 

 portions. Each of these portions grows outward into the form of a ball 

 connected with the surface by a short narrow stalk. This sphere 

 acquires a wall, and the process of spore-formation is completed. 



Class XXIV.— Acrasieae. 



So far as is known the spores of Acrasieae germinate only in nutrient 

 solutions. The swarm-spores are never ciliated, and move only by 

 creeping in amoeboid fashion. Under unfavourable conditions they 

 encyst themselves, and form temporary resting states. They unite in 

 great numbers for the purpose of forming spores again, but the union 

 nevei- amounts to coalescence into plasmodes. They are heaped together 

 as it were, and compose bodies of more or less definite form. In this 

 condition each swarm-spore becomes invested with a thin membrane, 

 though no common sporangial wall is formed. Guttulina (Cienk.) forms 

 simple spore-heaps, but in Dictyostelium (Bref.) and Acrasis (Van Tiegh.) 

 a stalk is formed by the swarm-spores in the centre of the mass becoming 

 transformed into series of cells with firm walls, and up it the rest of the 

 swarm-spores climb and form spores at the top. 



Doubtful Mycetozoa. 



De Bary repudiates the attempt made by Zopf to bring together 

 under this group an ill-assorted assemblage of lower organisms exhibit- 

 ing amoeboid movements. He considers such forms as Bursulla (Sorok.), 

 Protomyxa (Hseck.), Vampyrella (Cienk.), Nuclearia (Cienk.), Monas 

 amyli (Cienk.), Monadopsis (Klein), Pseudospora (Cienk.), Colpodella 

 (Cienk.), and Plasmodiophora (Woron.) to be doubtful Mycetozoa. 

 Plasmodiophora Brassicse (Woron.), which is parasitic on the roots 

 of Cruciferse, on which it produces large swellings, is common. The 

 ciliated swarm-spores penetrate into the parenchymatous tissue of such 

 roots. The cells affected swell to a great size, and large amoeboids 

 appear in them, but it is not certain whether these are single swarm- 

 spores or small plasmodes formed by the coalescence of several. The 

 whole protoplasmic contents of a cell then break up into spores. 



Affinities. 



De Bary, to whose remarkable investigations we owe the bulk of 

 our knowledge of the Mycetozoa, considers that the group differs 



