96 
B. Muriel Bristol. 
Name 0 / Date of 
Plot. Collection. 
Alga Found. 
Barnfield* 1870 
(10% water-content) 
Barnfield* 
Plot la. 
Hoosfield* 
1870 
1868 
Geescroft 1865 
Chlovococcum humicola (Naeg.) Rabenh. 
Stichococcus bacillar is Naeg. 
As from last sample above. 
Trochiscia aspera (Reinsch) Hansg. 
Chlovococcum humicola (Naeg.) Rabenh. 
Nostoc muscorum Kiitz. 
Chlovococcum humicola (Naeg.) Rabenh. 
It was hoped that a comparison of the algae found in the 
various Broadbalk soils would indicate in what order the different 
species were eliminated by successively increased periods of drought. 
The results, however, are not sufficiently regular to admit of this to 
any great extent, though in a few cases some deductions may be 
made; for this purpose the following comparative table (p. 97) is useful. 
It is very conspicuous that the Broadbalk 1865 sample con¬ 
tains far fewer species than the sample collected from the same 
field nine years earlier; this difference cannot be due to the 
relative periods of drought, hence some other factor or factors 
must have been at work in eliminating certain of the species, since 
it is scarcely likely, in view of the much more uniform results 
obtained from the other samples, that the discrepancy has arisen 
from the absence of the algae from the soil at the time of its 
collection. It is possible that such a factor is the degree of 
dryness of the soil during the period of storage. Unfortunately 
no exact information on this subject is available, but the theory 
is supported by the fact that the sample containing the greatest 
amount of water in 1912 was that collected in 1868, and this 
sample is the one from which the largest number of species have 
been obtained. The sample collected in 1846 differs from the others 
in that in about 1880 the bottle was opened and the soil spread out 
in a warm room to finish drying, so that when it was bottled again 
it contained only 3% of water. The presence of only two species of 
algae in this soil may therefore be due not only to the great age of 
the soil but also to the extremely low water-content of the soil. 
In the case of Chlovococcum humicola, the presence of this alga 
in all the cultures except those of the 1846 Broadbalk sample seems 
to indicate that its power of retaining its vitality in these old soils 
is more or less independent of their water-content, hence it is 
* These soils also contained moss protonema. 
