100 
B. Muriel Bristol. 
mermann 1 describes the cells as shortly barrel-shaped or cylindrical, 
and in many filaments of the cultures this is the case; there can 
be observed, however, a tendency of the cells of other filaments to 
become rounded off from one another and to assume a somewhat 
more spherical form. It is likely that small differences such as 
these are the result of the treatment to which the algae have been 
subjected, and are not to be regarded as of specific importance. 
A different form of N. muscorum was found in the 1881, 1869, 
1856 and 1846 Broadbalk samples and in the Hoosfield sample, and 
this differs much more considerably from the typical form. The 
vegetative cells are usually almost spherical, 3—3‘5/a in diameter, 
though in some filaments the typical barrel-shaped cells can be 
Fig. I. Nostoc muscorum Katz, forma, v. vegetative cells, h, hetero¬ 
cysts, s. spores, g.s. germinating spore. 
observed, and in this case are 3-4/a in length. The heterocysts 
are infrequent, and are generally very much smaller than in the 
typical form, rarely exceeding 4-5/a in diameter, though occa¬ 
sional hetercysts have been found measuring 5‘5-6/a in diameter. 
The spores are oval, 4-5/a broad, by 7-8‘5/a long, and grow in long 
irregular chains of a very characteristic form, as is shown in Text- 
Pig. 1. The walls of the spores are smooth and shiny, and become 
at first yellowish and later a darker brownish colour. 
In those cultures in which both of these forms of N. muscorum 
occur, viz., in those of the 1881 Broadbalk soil, other forms 
’ Lemmermann, E. Kryptogamenflora der Mark Brandenburg III, 
Algen I, p. 168, Leipzig, 1910. 
