ORDER MYXOGASTRALES OR SLIME MOLDS 



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A B 



Fig. 2. Myxogastrales. Didymium squamulosum (A. & S.) Fr. (A) Plasmodium. (B) 

 (B) Sporangium. (Courtesy, D. M, Cayley.) 



modium creeps through the soil or rotten wood or decaying vegetable 

 matter, fruiting bodies of fungi, etc., digesting the food suitable for it 

 and increasing in size and in the number of contained nuclei. Howard and 

 Currie (1932) showed that the plasmodia of various species of slime molds 

 destroy the mycehum and sporophores of many types of Hymeno- 

 myceteae with great rapidity. On the other hand some species can be 

 grown very successfully upon various standard culture media. Eventually 

 it emerges as a fine or coarse network upon the surface of the substratum. 

 It may be lobed and exhibit a continual creeping motion in various direc- 

 tions. In diameter it may vary from a few millimeters up to 15 or 20 

 centimeters, and in color from white to yellow, orange, red, brown, 

 violet, and other colors. Camp (1937) showed that it contains true con- 

 tractile vacuoles. Food is obtained by invagination, the lining of the food 

 vacuole being a portion of the original external surface of the Plasmodium. 

 Eventually the Plasmodium heaps itself up somewhat, on the exterior 

 of its substratum, or even creeps up adjacent objects, and there undergoes 

 the changes which lead to the production of the fructifications. These 

 may be separate from one another or may be crowded together into a 

 compound structure. In the Suborder Endosporeae there appears ex- 

 ternally, a noncellular peridium secreted by the Plasmodium. This may 

 be of various thicknesses according to the species, and may or may not 

 be encrusted with lime. Within the fructification are secreted numerous 

 noncellular threads and beams which form a sort of framework. This is 

 the capillitium. Its structure and arrangement are of great value in 

 classifying this difficult group of organisms. Between the threads of the 

 capillitium, usually following simultaneous meiotic divisions of all nuclei 

 of the Plasmodium, the protoplasm rounds up into innumerable small 

 uninucleate cells which secrete cell walls. In Physarum polycephalum it 



