98 
B. Muriel Bristol. 
The two algae with the greatest power of resistance are 
Nostoc inusconun and Nodularia Harveyana whose spores germin¬ 
ated after a period of desiccation extending over seventy years, 
during the last half of which the soil contained only 3% of water. 
That the degree of dryness of the soil during the period of 
desiccation affects Stichococcus bacillaris is clear from a comparison 
of the Barnfleld samples. The alga was present in the cultures of 
all the samples obtained from the original bottles in 1916, the 
water-content of these being about 10%, but it was absent from the 
cultures of the samples which had been taken in 1912 and which 
in 1915 contained only 3*3% of water. The fact of its occurrence 
in only one of the Broadbalk samples, that containing the greatest 
percentage of water, may perhaps be explained in the same way. 
The absence of Plectonema Battersii and of Hapalosiphon 
flexuosus forma (?) from all the earlier Broadbalk soils, irrespective 
of their water-content, probably indicates that 48 years is very 
near the limit of the period during which they are able to retain 
their vitality. 
III. Descriptive notes on the species found. 
A. Bacillarie/E. 
Nitzschia Palea (Ktz.) W. Sm. 
This is the only diatom found in the cultures of these old 
stored soils, and was obtained from the Agdell sample ; it had thus 
retained its vitality for a period of nearly fifty years. The speci¬ 
mens examined agree in all particulars with the description given 
by Van Heurck, 1 except in habitat which is said to be aquatic 
Petersen, 2 however, has also found it growing on the surface of the 
ground in Denmark, so that the species is evidently not entirely 
aquatic in habit, as has generally been thought. 
B. Chlorophyce^. 
Trochiscia aspeva (Reinsch) Hansg. 
The alga described under this name is not exactly typical in 
character but can probably be regarded only as a cultural form of 
the species. Though the alga agrees in essential points of 
structure and life-history with the typical form, the cell-wall 
exhibits considerable variation in its markings. Some individuals 
' Van Heurek, H. Traite des Diatomees, p. 401, Anvers, 1899. 
Petersen, J. B. Studier over Danske ASroflle Alger, p. 295, D. Kgl. 
Danske Vidensk. Selsk. Skrifter, 7 Raekke, Nat. og Matheinatisk Afd. XII, 
7. 1915. 
