INTRODUCTION 7 



the young plasmodium, thus confirming in part Cienkowski's observa- 

 tions. 



At any time after germination of the spores, unfavorable conditions 

 may cause the swarm-cells or myxamcebae to cease their activities. 

 Each becomes surrounded by a hyaline wall, forming a microcyst, 

 which remains dormant until favorable conditions again appear, when 

 it gives rise to a swarm-cell. 



The determination of the manner of the multiplication of the 

 nuclei in the plasmodium has offered certain difficulties. Many years 

 ago J. J. Lister (A. Lister, 1893) demonstrated mitotic division of the 

 nuclei in Badhamia utricularis and since that time there have been 

 occasional observations in other species. So many attempts to secure 

 this stage failed, however, that there arose a widespread belief that 

 many of the divisions must be amitotic. Both Schunemann and 

 Howard (1932) have recently shown that division may be completed 

 within twenty minutes or half an hour and that it occurs nearly 

 simultaneously throughout a large plasmodium. This demonstration 

 explains why so many attempts to find it have failed. There is no 

 reason to doubt that indirect nuclear division is the rule and that 

 direct division rarely, if ever, occurs. 



In a number of cases the food of the plasmodium is known to con- 

 sist of solid material. As early as 1877, A. Lister observed that the 

 Plasmodium of Badhamia utricularis was parasitic upon a species of 

 Corticium, publishing his notes upon the behavior of this species and 

 of Brefeldia maxima in 1888. Physarum polycephalum has been repeat- 

 edly grown upon the hymenium of agarics in the laboratories of the 

 University of Iowa since the 90's. A number of other instances of 

 proved or suspected parasitism upon the hyphae and hymenia of the 

 higher fungi have since accumulated. These are summarized by 

 Howard and Currie (1932) who add extensively to the number, list 

 fifteen species known to be parasitic, and report extensive experiments 

 using a wide range of Hymenomycetes as substrata. Several species 

 have been grown in pure culture; among others, Didymium difforme 

 (Skupienski, 1926, 1927, 1928) and Didymium nigripes (Cayley, 1929). 

 F. A. Gilbert (1928) has shown that the swarm-spores of Dictydia- 

 ihalium plumbeum may be nourished not only by soluble material but 

 by bacteria and the spores of fungi. Watanabe (1932) experimented 

 with seventeen species of slime molds and sixteen species of bacteria 

 and found that all the slime molds could utilize bacteria to some 

 extent as food but that there was great variation in the range of 

 bacteria acceptable to different species, and in the reactions of the 

 slime molds to them. 



