CH. VIII. — MORPHOLOGY AND COURSE OF DEVELOPMENT. —ACRASIEAE. 441 



always roundish in form when saturated with water, but as they dry they often become 

 concave or boat-shaped, like the spores of many Fungi (see page 106). They are 

 provided with an episporium, a thick unstratified membrane which in a few cases, as 

 in Trichia fallax and some species of Didymium, is two-layered, and is provided in 

 many species with a thinner spot which is perforated in germination and may there- 

 fore be termed a broad germ-pore. The outer surface of the membrane is smooth or 

 furnished with projections of definite shape (Figs. 192, 193) according to the species 

 and genus, and is usually of a deep colour, being violet or violet-brown for instance 

 in all Calcareae and Stemoniteae, and yellow and red in the Trichiaceae. The pro- 

 toplasm enclosed by the episporium has been already described. 



As regards the material composition of the membrane in sporangia, 

 capillitium and spores, we know that it behaves towards reagents in a similar 

 manner to cuticularised plant-cell-membranes and to spore-membranes in the Fungi, 

 but analyses of it are still wanting. The blue or violet colour of cellulose with 

 iodine does not usually appear; but Wigand and myself found exceptions to this 

 rule in Trichia furcata, Wigd., T. pyriformis and T. varia, in which the innermost 

 layers of the walls of young sporangia become a dirty blue with iodine and sulphuric 

 acid ; the membranes also of the spores and of the cells which fill the stalk of Arcyria 

 cinerea, A. punicea and A. nutans and those of the spores of Lycogala epidendron all 

 turn a beautiful blue with the same reagents. Further details will be found in the 

 special treatises which will be named below. 



In the foregoing account of the Myxomycetes the nomenclature which Rostafinski 

 introduced in his monograph has been substituted for the older nomenclature, or 

 unequivocal synonyms only of Rostafmski's names have been retained. The most 

 frequently recurring names are : 



Calcareae = Physareae of my earlier works. 



Fuligo varians = Aethalium septicum of former authors. 



Perichaena liceoides = Licea pannorum, Cienk. 



Chrondrioderma dirlorme = Didymium Libertianum, Fres.,the ' Physarum album ' 



of Cienkowski. 

 Licea flexuosa = Licea serpula, Fr., &c. 

 Further details respecting the nomenclature and the structure of the spore- 

 receptacles should be sought in Rostafmski's writings : see also Just's Jahresbericht, 

 for 1873. 



ACRASIEAE. 



Section CXXIII. The Acrasieae, which live on the excrements of animals and on 

 decaying parts of plants, commence their development like the Myxomycetes with the 

 escape of a swarm-cell from a spore. The swarm-cell always remains in the form 

 which has amoeboid creeping movements, never assuming that which has cilia and 

 the hopping movement. After multiplying greatly by successive bipartitions the 

 swarm-cells unite again, many hundreds in number oftentimes if the development has 

 been vigorous, in order to form spores. But they do not for this purpose coalesce 

 into plasmodia. The swarm-cells are piled up one on another without coalescing, 

 remaining distinct and artificially separable from one another though closely crowded 

 together, and forming bodies of definite shape which rise perpendicularly above the 

 surface of the substratum, and in which every one or the majority of the swarm-cells 

 assumes the structure of a spore of a Myxomycete, having usually a delicate membrane 



