384 BOTANY PART n 



haploid amoebae, but these are digested within vacuoles (Fig. 314 D}. Ultimately 

 the plasmodium proceeds to form 'the fructification. The diploid nuclei of the 

 plasmodium undergo repeated mitotic divisions (Fig. 314 E). Their last division 

 shortly before the delimitation of the spores is a heterotypic division, in which 

 the chromosomes are reduced to the half number. Each haploid nucleus thus 

 formed becomes the nucleus of a spore. The nuclei not employed in spore- 

 formation degenerate. In Ceratiomyxa the spores may include a degenerating 

 nucleus as well as the normal one. From the latter by two successive divisions 

 four nuclei are formed and are present in the ripe spore. Another division occurs on 

 germination, so that ultimately eight swarm-spores are produced from each spore. 

 In the structure of their swarm- spores and myxamoebae the Myxomycetes show 

 their derivation from organisms of the nature of the Flagellata. Plasmodial 



fusions are also known among 



/'- - .. ^ Flagellates. 



/ '* g ./K Very large plasmodia, often 



\ over a foot in breadth, of a 



yK bright yellow colour and creamy 

 "^JgflS*\\ consistency, are formed by Fuligo 

 f -"',' LJf varians (Aethalium septicum), 



\-%S m an d as the "flowers of tan" are 



* ;i often found in summer on moist 



J^A tan bark. If exposed to desicca- 



tion, the plasmodia of this Myxo- 

 mycete pass into a resting state, 

 and become converted into spheri- 



*' -"jJ-K / 7 cal or strand-like SCLEROTIA, from 



' / / which a plasmodium is again pro- 



K, ^ / - duced on a further supply of 



'. Q K - /^ ' " water. Finally, the whole plas- 



\,, ^ modium becomes transformed 



into a dry cushion- or cake-shaped 



FIG. 314. Physarum didermoides. A, B, Amoebae in fructification of a white, yellowish, 

 process of division ; C, conjugation of two haploid or b rown co lour. The fructifica- 

 amoebae ; kk, the two uniting nuclei; D. binucleate ,- . ,, . . 



plasmodium with a haploid amoeba enclosed in a tion, m this instance, is enveloped 

 digestive vacuole ; E, plasmodium with six dividing "7 an outer calcareous crust or 

 nuclei (fcj) and with digestive vacuoles. (After JAHN.) rind, and is subdivided by numer- 

 ous internal septa. It encloses 



numerous dark violet-coloured spores, and is traversed by a filamentous capillitium, 

 in which are dispersed irregularly-shaped vesicles containing granules of calcium 

 carbonate. A fructification of this nature, or so-called aethalium, consists, there- 

 fore, of a number of sporangia combined together, while in most of the Myxomy- 

 cetes the sporangia are simple and formed singly. 



The structure and nature of the sporangia afford the most convenient means 

 of distinguishing the different genera. The usually brown or yellow sporangia are 

 spherical, oval, or cylindrical, stalked (Figs. 311, 312 D) or not stalked (Fig. 

 312 A}. They usually open by the rupture of the upper portion of the sporangium 

 walls, the lower portion persisting as a cup (Figs. 311 B, 312^4). In Cribraria 

 (Fig. 311 C) the upper part of the wall of the sporangium, which contains no 

 capillitium, becomes perforated in a sieve-like manner. In Stemonitis (Fig. 311 

 A] the whole peridium falls to pieces, and the capillitium is attached to a 

 columella, which forms a continuation of the stalk. 



(ft 



