8 THE MYXOMYCETES 



To speak of such organisms as saprobes is obviously inaccurate. 

 In many species the plasmodium spends its life within the tissues of 

 decaying wood, probably feeding partly on bacteria, fungous hyphae 

 and spores and perhaps protozoa; in a considerable number of species 

 the plasmodium may be found on the surface of decaying leaves or 

 fragments of woody debris. Very early in its development, the plas- 

 modium begins to manifest its tendency to become divided into vein- 

 like branches which redivide and then become reunited to form a 

 more or less fan-shaped network with a continuous layer of protoplasm 

 at the advancing margin. The structure of the plasmodium is not 

 uniform; there is an outer, hyaline region surrounding the inner gran- 

 ular portion and it is in the latter that the nuclei are found, so that 

 the outer portion seems to perform essentially the functions of the wall 

 of the thallus in one of the larger Phycomycetes. The protoplasm of 

 the interior exhibits a series of pulsating movements, flowing first in 

 one direction, then in the other, but the movement is always a little 

 stronger in the direction in which the plasmodium as a whole is mov- 

 ing. As it progresses over the substratum a shell of waste material 

 and secreted matter is left, marking the position of the principal veins 

 and suggesting collapsed hyphae. 



Because of the ease of securing relatively large amounts of proto- 

 plasm free from cell-walls and other skeletal material, the plasmodia 

 of slime molds have often suggested themselves as favorable material 

 for the chemical study of protoplasm. Kiesel (1930) points out that 

 the auxiliary and associated materials ordinarily used in other cells 

 for accessory purposes are present in plasmodia; hence the assumption 

 that plasmodia exhibit more pure protoplasm than other cells or proto- 

 plasmic masses is without adequate basis. Because, however, the 

 associated materials are incorporated in the general mass, the colloidal 

 elements of the protoplasm are exposed and easily accessible. 



In color, the plasmodia vary from hyaline or white through yellow, 

 orange, red, violet, blue, green and brown. Pallid grays, yellows and 

 browns are perhaps the commonest colors. While the color of the 

 Plasmodium is fairly constant for a given species, it is subject to con- 

 siderable variation, even in the same plasmodium, upon different 

 substrata and at different stages of development. Hence, while plas- 

 modial color is of some value as a taxonomic criterion, it must be used 

 with caution. Solacolu (1932) has shown that the myxomycete pig- 

 ments have the properties of anthracenes, which are of common 

 occurrence in fungi as in plants, but of doubtful occurrence in animals. 



The changes through which the plasmodium passes in becoming 

 transformed into a fructification have been followed in a number of 



