62 
Bristol. — On the Alga-Flora of some Desiccated 
occasional heterocysts were found whose diameter was as much as 6 ju. The 
spores were formed in series and were oval with smooth pale-yellow walls ; 
they were 4-5 to 5 jot broad and 6 to 7 11 long. 
11. Nodular ia Harvey ana, (Thwaites) Thuret. 
The form of this alga, which appeared in four of the samples, very 
closely resembled that already described from the old stored soils from the 
Rothamsted Experimental Station, 1 but was somewhat larger. 
The vegetative cells were barrel-shaped, about 4 to 6 ju broad and about 
half as long. Heterocysts were completely absent, and the spores were 
sub-spherical and about 8 fx in diameter, or oval and about 9 /1 broad by 11 to 
] 5 F long, usually about 13/^. There was frequently a distinct mucous 
12. Anabaena variabilis , Kuetz. 
This species occurred only 
in one soil-sample, and is recorded 
here for the first time from the 
British Islands. The vegetative 
cells were barrel-shaped, 4*5 to 6 \i 
broad, and usually shorter than 
broad, with slight constrictions be- 
tween the cells. The heterocysts 
were spherical or subspherical and 
6-5 to 7 jot in diameter. The spores 
were 7 to 9 -5 jot, broad and 8 to 15^ 
long, with smooth yellowish-brown 
walls ; they grew in series, but were 
to be found sometimes separated 
from and sometimes adjacent to the heterocysts, so that the form in the 
cultures was not exactly typical in this respect. 
13. Anabaena inaequalis , (Kuetz.) Born, et Flah., forma. 
A somewhat large form of this alga was found in five of the soils. 
The filaments were almost straight and parallel and were usually loosely 
entwined to form an extensive stratum. The vegetative cells were shortly 
barrel-shaped, 5 to 6 jut broad, and about 4 jut long, with slight constrictions 
between the cells. The filaments gradually tapered towards the end, and 
the end cell was rounded. The heterocysts were spherical and 6-5 to 8 jot in 
diameter; and the spores were cylindrical, 8 to 9 jot broad, and 14 to 18 jot 
long, with smooth yellowish walls. The spores were formed singly or in 
series of two, three, or as many as six, either adjacent to or apart from the 
heterocysts. This alga, though differing in dimensions from the typical 
form, agrees so much more nearly with it than with any other described 
species that it can only be regarded as a form of this species. 
1 Bristol, B. M. : loc. cit., 1919. 
sheath surrounding the filament. 
Text-fig. 6 . Nostoc minutum , Desmaz. 
a., vegetative filaments; b ., spore-formation, 
x 825. 
