60 Bristol . — On the Alga-Flora of some Desiccated 
occasionally a slight constriction between the cells could be observed, but 
this was not general. This species has previously been recorded only from 
running water, where it grows attached to water-plants, hence its appearance 
from the soil-samples is surprising. 
6. Nos toe muscorum , Kuetz. 
This species was obtained from five soils, but, possibly owing to 
cultural conditions, it differed slightly from the typical form. Young 
colonies were globular, with closely matted filaments coiled in loops towards 
the periphery of the colony, where the sheaths of the individual filaments 
could be distinguished. The whole was surrounded by a firm mucous 
sheath that gradually became light brown in colour. The colonies retained 
this form until they were ioo to 200 /x in diameter, but sooner or later they 
split to form an expanded leaf-like stratum in which the characters of the 
filaments could be distinguished. The cells were spherical or shortly barrel- 
shaped, 3 to 5 fx broad ; the heterocysts almost spherical and 5 to 7 jx 
broad ; the spores 6 to 8 /x long by 8 to 9-5 /x broad, arranged in long chains 
and possessing smooth yellowish walls. 
7. Nostoc foliaceum, Mougeot. 
A blue-green alga that could definitely be identified as this species 
was obtained from only two soils, but a form very closely resembling it was 
obtained from two others and may be merely a cultural form of the same 
species. In the first of these two forms the young colonies were spherical or 
irregularly elongated, consisting of filaments densely woven together and 
surrounded by a definite mucous sheath which gradually became yellowish- 
brown in colour. Later the colonies expanded to form flat and somewhat 
diffuse strata of more loosely entwined filaments. The vegetative cells 
were spherical or shortly barrel-shaped and 4 to 4-5 /x broad ; but heterocysts 
were never formed in the cultures, and the spores were rather smaller 
than is typical for the species, being only 5*5 to 7 jx broad by 6-5 to 
10 /x long. 
In the second form the general features of the colonies were very 
similar to those of the first, but the vegetative cells were shortly barrel- 
shaped and 5 to 6 /x broad, while such few heterocysts as were formed in the 
cultures were exceedingly small, being only 4 to 5 /x in diameter. This 
reduction in size and frequency of the heterocysts appears, however, to be 
a fairly common character in cultural forms, and therefore too much 
importance cannot be attached to it. The spores occurred in large masses 
and were oval or subspherical, about 6 to 9 /x in diameter. This is the first 
time that the species has been recorded from Great Britain. 
8. Nostoc commune , Vaucher (Text-fig. 4 ). 
Forms of this species were found in three arable soils. In the first 
form (a) the vegetative, cells were barrel-shaped, 4 to 6 jx in diameter, and 
the heterocysts subspherical and about 6-5 /x in diameter. Spores were 
