INTRODUCTION 9 



species, and while the details vary there is much that all the species 

 studied have in common. Bulliard, as far back as 1791, noted and 

 illustrated certain external features of this process but it was not until 

 1859 that de Bary attempted to trace the details in the case of Fuligo 

 septica. Recent careful studies combining morphological and cy to- 

 logical detail are those on Reticularia lycoperdon and Physarum poly- 

 cephalum already cited. The process varies somewhat, depending 

 upon the nature of the fructification, whether plasmodiocarpous or 

 sporangiate. 



An athalium may be defined as a slime mold fructification in 

 which all or a considerable part of a given Plasmodium is involved, 

 and in which differentiation has not proceeded to the delimitation 

 of separate sporangia. It must, therefore, be distinguished from a 

 pseudo-aethalium, as found in species of Tubifera and species such as 

 Stemonitis confluens, where the sporangia are delimited but borne in 

 compact and more or less attached groups. 



The plasmodiocarp may tentatively be regarded as less primitive 

 than the aethalium because it merges into the sporangiate type of 

 fructification. Further investigation may show, however, that it is 

 more primitive, and that both the sporangiate and aethalioid types 

 represent modifications of the plasmodiocarpous. In the typical 

 manifestations of the plasmodiocarp, as illustrated, e. g., by Physarum 

 serpula or Hemitrichia serpula, the protoplasm is aggregated into a 

 few of the larger veins as they rest upon the surface of the substratum, 

 and there becomes transformed into a fructification which has the 

 interior structure of a sporangium, but which retains the netted form 

 and outline of the Plasmodium. In species with distinct sporangia the 

 Plasmodium often assumes such a netted form before breaking up 

 into the primordia of the sporangia. The plasmodiocarp tends to 

 become shorter and less branched and thus merges by gradual degrees 

 through linear and pulvinate fructifications into the sporangiate 



fc yp e - . . c 



The sporangium is typically an erect fructification of definite form 

 and structure for a given species, each sporangium representing only 

 a small part of the protoplasm of a given plasmodium, hence sporangia 

 tend to be grouped in clusters or extensive masses, the entire group 

 representing the area occupied by the fruiting plasmodium. Dis- 

 carded remnants of the plasmodium usually remain at the base of the 

 sporangia, forming the hypothallus; sometimes in definite sheets, as 

 in the stemonites, less definite in the lower layer of plasmodiocarpous 

 or aethalioid fructifications. In Diachea leuco podia it appears as the 

 arrested network of the fruiting plasmodium. In other species, repre- 



