English Soils : an Important Factor in Soil Biology . 79 
zoogonidia-formation were observed, four zoogonidia being produced within 
a cell, but these were never seen to acquire cilia or to escape from the cell, 
and it is possible that the cultural conditions were such as to preclude this 
form of multiplication, 
VI. Summary. 
The investigation by means of water-cultures of forty-four samples of 
soil from widely separated localities has shown that there is a widely 
distributed ecological plant-formation in cultivated soils consisting of 
moss protonema and algae. The most important algae in this formation 
are : Hantzschia amphioxys, (Ehr.) Grun., Trochiscia aspera, (Reinsch) 
Hansg., Chlorococcum humicola , (Naeg.) Rabenh., Bumilleria exilis , Klebs 
and to a less degree Ulothrix sub tills , Kuetz., var. variabilis , (Kuetz.) Kirchn. 
Other species of typical soil-algae occurring somewhat less frequently give 
rise to smaller plant-associations within this formation. 
The total number of species and varieties found in these soils is sixty- 
four — -20 Bacillarieae, 24 Myxophyceae, and 20 Chlorophyceae. The soil- 
samples had all been subjected to complete desiccation for 4 to 2 6 weeks 
before being placed in the cultures ; hence these species could be expected 
to withstand any period of drought that might occur naturally. 
It seems likely that this extensive algal formation must be of consider- 
able economic importance in the biology of the soil. 
Six new species or varieties are described, sixteen species already 
described are newly recorded for the British Islands, and a number of new 
or interesting stages are depicted in the life-histories of certain species 
already known, especially in connexion with the germination of the spores 
of some blue-green algae. The final section of the paper contains a short 
account of each of the species found in the cultures. 
In conclusion, the writer desires to express her thanks to a number of 
friends who assisted her in making the collection of soil-samples. In 
particular she wishes to acknowledge her indebtedness to Professor 
G. S. West for his valuable help, especially in the identification of the 
species, and for his unfailing encouragement throughout the course of the 
investigation. 
The Botanical Laboratory, 
University of Birmingham. 
