On the Retention of Vitality by Alga. 105 
be due to the absence of the alga from the original soil-samples 
rather than to the influence of drought on the spores themselves. 
Secondly, the alga as observed in these cultures shows a suppres¬ 
sion of one of the most characteristic features of the genus, viz., 
the regular and frequent occurrence of the heterocysts. In young 
filaments only are heterocysts to be found, and in these cases 
they agree in shape and size with the typical form. The 
vegetative cells are 3'5-5 /a broad and little more than half as long 
the spores are sub-spherical, about 7/x in diameter. 
Cylindrospermum licheniforme (Bory) Kiitz. 
This species occurred in the 1868 and 1856 samples of the 
Broadbalk soil, and the spores have consequently retained their 
vitality for a period of nearly sixty years. The spores are oval 
with flattened ends, and the walls assume a deep red-brown 
colour when ripe; they are 1 3— 1 5/x broad and 21-29/a long. The 
heterocysts are oval or sub-spherical, 6-7’5/a broad by 8-9 /a long. 
Plectonema Bcittersii Gomont. 
Up to the present time this species has been described only 
from sea-water, hence its appearance in the cultures of the 1868, 
1869, 1881 and 1893 samples of the Broadbalk soil is extremely 
surprising. The form that appeared in the cultures agrees in 
every particular, except that of habitat, with that of Tilden’s 
description of the species, and it is quite distinct from any other, 
hence it is probable that this species has a far wider distribution than 
has hitherto been believed. The cells of the filaments are usually 
about3/A broad and 2 /a long, with a firm thin colourless sheath. 
In view of its previously described aquatic habit, the power 
that this terrestrial form has exhibited of retaining its vitality in 
a dry condition for nearly fifty years is very remarkable. 
Hapalosiphon flexuosics Borzi forma. (?) 
In the cultures of the 1868, 1869, 1881 and 1893 samples of 
Broadbalk soil a species of Hapalosiphon appeared which seems to 
stand nearest to H. dexuosus Borzi, though it does not exactly 
agree with it. The difference of habitat is very marked, though 
this is not unique since an even greater difference was observed 
in the species Plectonema Battevsii Gomont; and it its ability to 
withstand dessiccation for forty-eight years is therefore extremely 
interesting. 
The alga is richly branched, and the branches may be either 
