Capillitium in Certain Myxomycetes . 13 
gelatine films by the contraction of the air and its absorption in the sur- 
rounding medium, suggest a very interesting possible parallel to the 
conditions and chemical changes taking place in the case of the forming 
capillitium. The materials of the capillitial wall are presumptively dis- 
sociation products of proteid, whether they are conceived as set free by 
secretion or by direct transformation. If the chemical changes resulting in 
the production of the solid elastic and hygroscopic capillitial thread out of 
the watery colloidal cytoplasmic mass involve a reduction in volume we 
should have tensions set up similar to those produced about the contracting 
air bubble in the gelatine film. The formation of vacuoles as the initial 
step in the development of the thread may be regarded as conclusive proof 
that the production of the solid materials of the wall of the thread involves 
the setting free of water which at first may contain considerable quantities 
of dissolved transition products. As noted, these dissolved materials are 
apparently used up finally in the process of building the thread. 
Our knowledge of the chemical character of the cell-walls in the Slime- 
moulds is quite fragmentary. Wigand and de Bary (2) reported the common 
tests for cellulose in the case of the inner layer of the wall of the sporanges 
of Trie hia varia^furcata , and pyriformis , and in the spore- walls of Arcyria 
cinerea ) p unice a ^ and nutans and Ly cog ala epidendron. More recent work 
on the colour reactions of chitin and its derivatives with iodine leaves these 
results uncertain. 
The work of Wisselingh (45) and still earlier authors gives sufficient 
proof that chitin is a widely occurring constituent of fungus cell-walls, but 
that cellulose is also characteristically present in certain cases. In the Slime- 
moulds Wisselingh (45) reports cellulose as present in the spore-walls of 
Didymium squamulosum, chitin in the spore-walls of Plasmodiophora brassicae , 
and neither in the spore-walls and membranes of Fuligo septica . Scholl (41) 
has made careful studies of the methods of isolating chitin from Boletus 
edulis , and there can be no question that the plant and animal material are 
essentially similar in their chemical characteristics. 
Wisselingh (45) believes that chitin and cellulose do not occur together, 
and gives evidence that other unknown elements may be associated with 
chitin in fungus cell-walls. Not enough is known as to the actual chemical 
constitution of chitin to give a basis for a conclusion as to the method of its 
formation in the capillitial vacuoles, even in case it is found to be an essential 
constituent of the thread. The available evidence (40), (12), (4 a) indicates 
that fundamental similarities between the method of its deposition and 
that of cellulose are to be expected. Czapek (8) suggests that glyco- 
proteids are perhaps to be assumed as the sources of cellulose. As 
noted, our own observations show that the young capillitial threads have 
the same selective affinity for orange G as is observable in the young 
cellulose walls of the higher plants. Conclusions based on microchemical 
