English Soils: an Important Factor in Soil Biology. 37 
whether in this country there exist many algae that are sufficiently resistant 
to desiccation to be able to persist in the soil during any period of drought 
that might naturally occur. The investigation was begun in September, 
1 915, when a collection was made of small samples of cultivated soils from 
different parts of the country. The samples were taken from arable land or 
from old gardens, in such places as appeared to be destitute of vegetation, 
and were then spread out to dry gradually in a warm room for at least 
a month, care being taken to prevent foreign infection of the soils by cover- 
ing them with sterile paper. This preliminary drying of the soils served to 
kill off any algae present that might be unable to resist prolonged desicca- 
tion and to induce any more resistant ones to enter into a resting state. 
When completely dry, the soil-samples were placed in small tin boxes for 
storage ; by this time the soil in almost every case had crumbled into 
a fairly fine powder. 
II. Cultural Methods.* 
Three cultures of each sample were made, with the exception of 
Nos. 5 and 35-40, of which there were only two. The cultures were set up 
in very carefully sterilized 1 vessels which comprised glass boxes and small 
conical flasks or wide-mouthed bottles closed with plugs of cotton-wool. 
Into each of the sterilized culture-vessels a sterilized culture-medium was 
introduced to a depth of about half an inch, and into this a few grammes of 
the soil to be examined were introduced by means of a sterilized spatula. 
The vessels were closed and placed under glass cases in a north window and 
left for some months to develop. 
The culture-solution most generally used was an aqueous mineral-salt 
solution having the following composition : 1 grm. KH 2 P 0 4 , 1 grm. NaN 0 3 , 
0-3 grm. MgS 0 4 , o-i grm. CaCl 2 , 01 grm. NaCl, a trace of FeCl 3 , 1,000 c.c. 
distilled water. 
But for the sake of comparison certain of the cultures were made with 
a solution diluted with distilled water to half the above strength, and others 
with sterilized rain-water. Evaporation from the surface of the cultured 
took place only slowly, and it was found sufficient, in order to keep them 
moist, to water them at the end of about six months with sterilized distilled 
water or with rain-water ; in one or two cases where the cultures were 
assuming a brownish colour diluted mineral-salt solution was added. 
The first signs of growth were observed in the cultures at about the end 
of November, when a thin white scum gradually appeared on the surface of 
the liquid, and was found on examination to consist' of bacteria. About six 
weeks later the scum began to assume a green tinge of colour, and small 
tufts of green filaments were observed to be growing from the soil at the 
1 All the culture-vessels were heated on three separate occasions to a temperature of about 
1 20 0 C., and kept at that temperature for three hours on each occasion. The culture-media were 
heated in a steam sterilizer for about three hours on each of three occasions. 
