English Soils: an Important Factor in Soil Biology. 55 
The physiological experiments of Boresch , 1 Schindler , 2 and 3 and 
Magnus , 2 showing that certain algae are able to build up chlorophyll and 
phycocyanin and to grow in the dark, provided that sufficient nitrogenous 
food material is available, appear to have an important bearing on the mode 
of life of soil-algae, and suggest that it is quite possible for algae not merely 
to exist passively in the lower layers of the soil, but also to carry on active 
growth, for some time at any rate. In order to test this possibility Esmarch 
carried out a series of experiments upon algae specially buried in the soil 
at a known date and available for microscopic examination at any time ; 
the cultures of the algae were kept in the dark. 
From these experiments Esmarch observed that the blue-green algae 
enclosed in the soil retained their normal colour for some time, but that 
after a shorter or longer period, depending on the composition of the soil 
and the species of alga, the filaments gradually lost their blue-green colour 
and finally became yellowish. At first the dimensions and appearance of 
the filaments remained unchanged and the cells appeared perfectly healthy, 
but after some time distortion and finally disintegration of the filaments 
took place, leaving only spores and heterocysts. 
He observed that Nostoc sp. had greater powers of resistance than 
Anabaena and Cylindrosperrnwn spp., and attributed this to the fact that 
the mucilaginous investments and cell-walls are much stronger and more 
permanent in the Nostoc species than in the others. 
Esmarch’s work is thus extremely important in that it shows that not 
only is there an extensive flora of blue-green algae in the top layers of the 
soil, but also that filaments of at least some of these algae are able to 
continue their vegetative functions below the surface of the ground for 
periods varying in individual cases from three .to six weeks, or even, as in 
the case of one Nostoc sp., as much as ten weeks. 
Estimations of the approximate numbers of algae present in different 
soils in relation to other organisms have not yet been attempted, but the 
large number of different species found in English soils rather suggests that 
the proportions would be high for this country. No recent sample of 
a cultivated soil has been investigated which yielded fewer than four 
different species, and only four samples yielded fewer than seven species ; 
many of the cultures were found to contain at least a dozen, while several 
yielded as many as seventeen or eighteen different species and varieties, in 
addition to the moss protonema which was obtained from every soil. It is 
inconceivable that such an extensive population of chlorophyll-containing 
organisms can be without its effect both on the other organisms in the soil 
1 Boresch : Die Farbung von Cyanophyceen und Chlorophyceen in ihrer Abhangigkeit vom 
StickstofFgehalt des Substrats. Jahrb. fur.Bot., lii, 1913, pp. 145-85. 
2 Magnus, W., and Schindler, B. : Ueber den Einfluss der Nahrsalze auf die Farbung der 
Oscillarien. Ber. der Deutsch. Bot. Ges., xxx, 1912-13, p. 314. 
3 Schindler, B. : Ueber den Farbenwechsel der Oscillarien. Zeitsch. f. Bot.,v, 1913, pp.. 553-5* 
