INTKODUCTION. 



FRIES gave the name of Myxoyastres, in 1833, to the group of 

 organisms described in this Monograph, placing it among the 

 Gasteromycetous Fungi. In 1836 Wallroth substituted the term 

 Myxomycetes (Schleimpilze) for the older name, and this came to 

 be the generally accepted designation. Later investigations showed 

 that the spores, instead of producing a mycelium, as in the case of 

 fungi, gave birth to swarm-cells^ which coalesce to form a plasmo- 

 diuin. In consequence of this discovery, which indicated a relation- 

 ship with the lower forms of animal life, de Bary in 1858 introduced 

 the name Mycetozoa. Under this head he still retained the term 

 Myxomycetes for the section so named by Wallroth, but linked with 

 them the Acrasiece of Van Tieghem, a small group inhabiting the 

 excrement of animals ; in these the spores are said to produce 

 sw T arm-cells, as in the Myxomycetes, w T hich multiply by division 

 but do not coalesce to form, a plasmodiurn. At a certain period, 

 when the fruits are about to be formed, they become attached 

 in branching strings which concentrate to a point, where they 

 are massed together in aggregations of more or less definite 

 shape ; the swarm -cells, however, do not lose their individuality. 

 In Dictyostelium, a genus of the Acrasiece, a stalk is formed by 

 the arrangement of a number of swarm-cells in vertical rows in 

 the centre of the heap ; the surrounding amreboid bodies creep 

 up this stalk and form a globose cluster at the extremity ; here 

 each amoeboid swarm-cell acquires a spore-wall, and they become 

 a naked aggregation of spores not enclosed by a definite sporangium- 

 wall. Rostannski followed de Bary in the view that the formation 

 of a plasmodiurn. indicates a wide separation in the natural 

 position of the Myxomycetes from the fungi, but he suppressed 

 that Dame entirely, adopting de Bary's class name Mycetozoa in 

 its place ; at the same time, he admitted into his Monograph 

 Dictyostelium, a genus of the Acrasiece. The reason for his including 

 this genus may be the fact pointed out by de Bary, that Brefeld 

 in first describing the dense aggregations of swarm-cells into the 

 stalked spore-masses of Dictyostelium, refers to them as being 

 " plasmodia ; that is, products of the coalescence of swarm- 

 cells ; " and it was not until after the publication of Rostafinski's 



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