SLIME MOULDS (mYXOMYCETES) 9 



stimulation of the host to form gall-hke swelUngs. The whole Plas- 

 modium is later transformed by division into a greater or less number 

 of parts, which become surrounded by membranes to form spores. 

 The spores are free in the cells of Plasmodiophora, while in SorosphcBra 

 and in Tetramyxa they are clumped, and surrounded by a delicate 

 membrane. The order includes a single family: 



Family i. Plasmodiophorace^. — ^The characters of this family are 

 coincident with those of the class as given above. The family includes 

 four genera distinguished as follows: 



A. Spores distinct from each other, irregularly aggregated and fiUing 

 the host cells. 



{a) Spores regular in shape, spheric, (i) Plasmodiophora. 



(b) Spores irregularly shaped, rod-like, or angular. (2) Phytomyxa. 



B. Spores united into clumps inclosed by a delicate membrane. 

 {a) Spores united in groups of four each. (3) Tetramyxa. 



(b) Spores in greater number, united into hollow spheres. (4) 

 Sorosphcera. 



The genus Plasmodiophora comprises possibly three species found 

 in Europe and America. They are parasites in the parenchyma cells 

 of the cortex of the roots of the higher plants, where they produce 

 gall-like swellings. The plasmodium fills some of the living cells of 

 the host. The spores formed subsequently are spheric and lie free 

 within the host cells. The best known species is P. brassicce which 

 is the cause of a serious disease known as club foot, or finger and toes 

 (Fig. i). The symptoms of the disease, the relationship of host and 

 parasite, will be described in a subsequent section of this book. Two 

 other species have been described, viz., P. alni in the roots of the alder; 

 and P. eleagni in the roots of Eleagnus, the silverberry. Considerable 

 more study will have to be made of the organisms in the roots of the 

 alder and silverberry before we can definitely place the causal organ- 

 isms. Tentatively, we may adopt the generally accepted view of the 

 systematic relationship of the two responsible organisms until later 

 investigation either proves or disproves the nature of the parasites 

 attacking Alnus and Eleagnus. 



The genus Phytomyxa is represented by two species which live as 

 parasites in the roots of Hving plants and cause tuber-like enlargements. 

 The Plasmodia fills the host cells, and later, the irregularly shaped 



