MYXOMYCETES 



403 



nourishes itself and grows, acquiring, in the case of some Physareae, great 

 dimensions, and forming reticulated masses which may be measured by 

 inches. Fuligo varians (Somm.) (or as it is more commonly called ^Etha- 

 lium septicum (Fr.) or * flowers of tan,' from its appearing during summer 

 on tan) is such a body, but the plasmodes of other families of Myxo- 

 mycetes, as well as of some Physareae, generally remain very small in com- 

 parison with this. The appearance of the strands or branches of the plas- 

 mode (under the microscope) is that of a turbid granular mass bordered 

 by a clearer hyaloplasm. The surface of the plasmode of Physareae is in- 

 vested with a soft shiny envelope of a substance different from protoplasm. 

 The plasmodes of certain other forms are similarly invested with en- 

 velopes, as to the nature of which not much is known. The larger portion 

 of the granules contained in the plasmodes of Physareae are of calcium 

 carbonate ; granules contained in other 

 plasmodes require investigation. Nuclei 

 are abundantly present. Many foreign 

 bodies such as spores, diatoms, &c., 

 are often found included in plasmodes. 

 Constant movement is maintained, and 

 the most characteristic is that of the pro- 

 trusion and retraction of pseudopodes. 

 Since protrusion is commonly more 

 active on one side than on the other, an 

 advancing movement of the whole is thus 

 brought about. Internal streamings, more 

 or less copious, answer to the amoeboid 

 movements. The external causes of move- 

 ments are : with reference to (i) illumina- 

 tion, they are negatively heliotropic ; (2) 

 water they are positively hydrotropic, 

 i.e., when not about to form spores they 

 leave comparatively dry spots and move 

 towards moist places ; ($)food they are 

 positively trophotropic, i.e., they move 

 towards nutrient substances (as might 

 be expected) ; (4) heat within certain 

 limits they move towards the warmer side 

 of a surface unequally warmed. These 

 movements are without reference to the 

 direction in space in which they may 



have to be made. It may be stated here that the process of nutrition 

 takes place only in the amoeboid states the swarm-cell and plasmode. 



FIG. 334. Stemonitis fusca Roth, 

 sporange (natural size). B, capillitium 

 (x about 100). (After Reinke.) 



