18 MYCETOZOA 



nuclei now divide by karyokinesis ;* the network of proto- 

 plasm then spreads out to form a continuous superficial 

 covering, which rapidly divides into polyhedral portions or 

 cells of equal size, each containing a single nucleus. The whole 

 sporophore is invested by a thin hyaline layer. The contents 

 of each cell now rise as a shortly cylindrical projection from 

 the surface of the sporophore, carrying with it a hyaline 

 investment, which becomes constricted at the base until an 

 elongated membranous stalk is formed, bearing at its apex 

 a globule, the young spore, consisting of granular proto- 

 plasm and a nucleus. This nucleus now divides twice by 

 karyokinesis. f The mature spore, an ellipsoid body enclosed 

 in a membranous wall, thus contains four nuclei. It is easily 

 detached from the stalk, and the gelatinous sporophore dries 

 to a membrane of the frailest structure, to disappear with the 

 first shower of rain. It is probable that the sporophores of 

 Ceratiomyxa may be regarded as representing the sporangia 

 of the Endosporeae. We have in both cases supporting struc- 

 tures and spore-plasm, the nuclei of which divide by karyo 

 kinesis shortly before the spores are formed. The mature 

 spore in Ceratiomyxa is more advanced than that of the 

 Endosporeae in that the nucleus has already undergone two 

 divisions within the spore. 



Distribution and Specific Characters. — The geographical dis- 

 tribution of many of the species is very wide, as might be 

 expected from the ease with which their minute spores can 

 be carried by currents of air. Some, however, appear to be 

 characteristic of warmer climates, such as Physarum roseum, 

 Physarella oblonga, Trichamphora pezizoidea ; while others are 

 usually found in alpine regions in the neighbourhood of 

 melting snow, e.g. Diderma niveum, Lepidoderma Carestianum, 

 Lamproderma violaceum var. Carestiae.% 



In England some species may occur at any season of the 

 year after moist weather, e.g. Physarum nutans, Craterium 

 minutum, Didymium squamulosum, Trichia varia ; others again 

 appear only in the summer and autumn, e.g. Physarum 

 psittacinum, Stemonitis herbatica, Dictydium cancellatum, and 

 most of those species that inhabit heaps of old straw. 



The main characters distinguishing the different species are 

 remarkably constant in sporangia gathered in all parts of 

 the world. Specimens of Hemitrichia clavata, H. Serpula, 

 Dictydium cancellatum, and Trichia decipiens, have been 



* See Jahn in Ber. Deutsch. Bot. Gesell., xxvia 342-352 (1908). t Jahn, op. cifc., 

 xxv. 25 (1907) ; Olive in Trans. Wise. Ac. Sci., xv. 753 (1907). 



t M. Meylan has published interesting observations on the species occurring at 

 different elevations and seasons in the Jura Mountains (see Bull. Soc. Vaud., xliv. 

 285-302, 1908). 



