ZFGOSPOREM. 



363 



creep about in troops, come into close contact with one another, and finally coalesce 

 into large lumps. As sodn as one of these lumps is formed, the rest collect from all 

 sides round it as a centre, coalesce with it, and increase in this manner the mass of 

 protoplasm which then becomes more and more rounded off. There is every reason 

 to believe that this collective union of zoogonidia is a conjugation and therefore a 

 sexual act, in the same sense as the conjugation of the zoogonidia of the Pando- 

 rineae ; and the large mass of protoplasm formed in this way, which is called a Plasmo- 

 dium, must therefore be treated as the analogue of the zygospore. The only difference 

 is that in this case the zygospore does not become invested with a cell-wall nor go 

 through a period of rest, but at once undergoes further development, becoming 

 transformed into a stalked fructification which produces a large number of spores. 

 In accordance with their mode of origin these spores may be compared not merely 

 with the zoospores developed from the zygospore of Pandorina, but also with the 

 ascopores of the Ascomycetes, and even with the spores of the Muscineae. The 

 formation of this fructification out of the roundish plasmodium of Dictyostelium com- 

 mences with the production in its centre by free cell-formation of a number of cells 

 each surrounded by a cell-wall of cellulose, which unite into a parenchymatous tissue 

 forming in the interior of the Plasmo- 

 dium a column or stalk standing erect 

 on the substratum. As this column con- 

 tinues to grow in height, the rest of the 

 protoplasm which surrounds it creeps 

 up it, and collects at its summit into 

 a round lump, the entire substance of 

 which now breaks up into a number of 

 spores. This example furnishes the 

 simplest case of the course of devel©p- 

 ment of a Myxomycete. In most other 

 instances it is much more complicated, 

 the development being more complete, 

 and a reduction to this plan becoming 



constantly more difficult. But the first ^IG. i^^.-Physarum album {after Cienskowski). 1 spore ; 



^ . 2 escape of its contents ; 3 the contents when free ; 4, 5 the same in 



stage of the development is essentially the form of a zoogomdium provided with a ciUum; 6,7 after loss of 



4.U^ ^„.^^ :„ «ll l\/T ^.«.,^^4.^„ TT^^U the cilium ; 9— ii coalescence of the amoeboid bodies ; 12 a small 



the same in all Myxomycetes. Each piasmod.um. 

 spore gives birth to from one to eight 



amoeboid bodies, which grow and multiply by repeated division, subsequently coalescing 

 with one another in large numbers and producing plasmodia. The plasmodia of other 

 Myxomycetes, however, do not at once produce fructifications, but maintain for a 

 longer period an independent life, creeping about in the moist interstices of their 

 substratum; as, for example, the yellow plasmodia inside a tan-heap, which at length 

 come to the surface, and then coalesce into the large bodies which are known as 

 * flowers of tan.' Other plasmodia creep about for a time on rotten wood or among 

 decaying leaves, at length in the same way reaching the surface, and then usually 

 producing simultaneously a number of fructifications. Fig. 172 ^ may give an idea of 

 the mode in which net-like structures are produced by these motions of the plasmodia. 

 The substance of the plasmodium is thin and granular in the interior and bounded on 

 the outside by a homogeneous pellicle ; it is constantly changing its form ; protuberances 

 arise at various spots which move onwards with a flowing and creeping motion, ramify, 

 and anastomose with one another, while the substance flows into them from behind, 

 and in this manner enables the entire structure to creep gradually forwards. Imme- 

 diately before the period when the fructification is produced, a tendency is manifested 

 to creep up erect bodies, so that finally the fructification is frequently found on 

 plants, stems, or leaves at a considerable distance from the original nutrient sub- 

 stratum. At this period the plasmodium collects at certain spots, and forms either 



