Chapter 17 

 Order 2 Mycetozoa de Bary 



THE Mycetozoa had been considered to be closely related to 

 fungi, being known as Myxomycetes, or Myxogasteres, the 

 'slime molds.' Through extended studies of their development, 

 de Bary showed that they are more closely related to the Protozoa 

 than to the Protophyta, although they stand undoubtedly on the 

 border-line between these two groups of microorganisms. The 

 Mycetozoa occur on dead wood or decaying vegetable matter 

 of various kinds. 



The most conspicuous part of a mycetozoan is its Plasmodium 

 which is formed by fusion of several myxamoebae, thus producing 

 a large multinucleate body (Fig. 135, a). The greater part of the 

 cytoplasm is granulated, although there is a thin layer of hyaline 

 and homogeneous cytoplasm surrounding the whole body. The 

 numerous vesicular nuclei are distributed throughout the granu- 

 lar cytoplasm. Many small contractile vacuoles are present in the 

 peripheral portion of the Plasmodium. The nuclei increase in 

 number by division as the body grows; the division seems to be 

 amitotic during the growth period of the plasmodium, but is 

 mitotic prior to the spore-formation. The granulation of the 

 cytoplasm is due to the presence of enormous numbers of granules 

 which in Calcarinea are made up of carbonate of lime. The Plas- 

 modium is usually colorless, but sometimes yellow, green, or 

 reddish, because of the numerous droplets of fluid pigment present 

 in the cytoplasm. 



The food of Mycetozoa varies among different species. The 

 great majority feed on decaying vegetable matter, but some, such 

 as Badhamia, devour living fungi. Thus the Mycetozoa are 

 holozoic or saprozoic in their mode of nutrition. Pepsin has been 

 found in the plasmodium of Fuligo and is perhaps secreted into 

 the food vacuoles, into which proteins are taken. The plasmodium 

 of Badhamia is said to possess the power of cellulose digestion. 



When exposed to unfavorable conditions, such as desiccation, 

 the protoplasmic movement ceases gradually, foreign bodies are 

 extruded, and the whole plasmodium becomes divided into 

 numerous sclerotia or cysts, each containing 10-20 nuclei and 



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