Chapter 18 

 Order 2 Mycetozoa de Bary 



THE Mycetozoa had been considered to be closely related to the 

 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 Myce- 

 tozoa 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 many myxamoebae, thus producing 

 a large multinucleate body (Fig. 179, 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 granular cytoplasm. 

 Many small contractile vacuoles are present in the peripheral por- 

 tion 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 some forms are made up 

 of carbonate of lime. The Plasmodium is usually colorless, but some- 

 times 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 protein materials are taken. The Plasmodium of Bad- 

 hamia 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 numer- 

 ous sclerotia or cysts, each containing 10-20 nuclei and being sur- 

 rounded by a resistant wall (6). These cysts may live as long as three 

 years. Upon return of favorable conditions, the contents of the 

 sclerotia germinate, fuse together, and thus again produce plasmodia 

 (c-e). 



When lack of food material occurs, the Plasmodium undergoes 



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