58 Bristol . — On the Alga- Flora of some Desiccated 
substance built up is greatly increased, while the loss of ammonia into the 
air is reduced to a minimum ; similar results were also obtained with soils 
in which higher plants were growing. Hence Gautier and Drouin regarded 
soil-algae less as factors in the acquisition of nitrogen by the soil than as 
agents for the transformation of the ammoniacal substances already present 
into more complex organic substances, and thus as factors in helping to 
bring about the nitrogen cycle of the soil. 
This consideration of the facts already ascertained indicates very clearly 
that the part that living algae play in the economy of the soil is no incon- 
siderable one, though the difficulties in the way of establishing direct 
evidence are very great, and much work will be necessary before any very 
definite statements can be made. It is, on the other hand, quite certain 
that by their death algae contribute very largely to the fertility of soils in 
that they present considerable quantities of organic material to the putre- 
factive bacteria for decomposition. 
The extraordinary property which moss protonema and many of these 
soil-algae possess, of being able to retain their vitality for very long periods, 
even under conditions of complete drought, has already been described 
elsewhere ; 1 and it is to be emphasized in this connexion that all of the 
forms which exhibit these powers build up considerable quantities of a fatty 
oil in their cytoplasm, so that the chemical energystored up in them is very 
high, and their value as sources of energy for other organisms correspond- 
ingly great. In the cultures under observation certain protozoa have been 
observed to feed quite extensively on soil-algae, specimens being frequently 
found containing a dozen or more inclusions that might be either diatoms or 
green algae, or more rarely blue-green algae. Whether this condition exists 
in nature or is merely an accident due to the presence of a greater amount 
of water than is usually available under natural conditions in the soil it is 
impossible to say, but it is probable that algae may also contribute largely 
to the nutrition of some of the lower organisms of the soil, and especially of 
worms. 
Again, if algae are present in any quantity in a soil, their physiological 
functions of respiration and photosynthesis must have a certain effect upon 
the nature of the gases in the soil, while their mucous investments probably 
play an important part, especially in sandy soils, in helping the soil to retain 
its moisture. 
1 Bristol, B. M. : (a) On the Remarkable Retention of Vitality of Moss Protonema. New Phyt., 
vol. xv, No. 7, July, 1916, p. 137. 
(< 5 ) On the Retention of Vitality by Algae from Old Stored Soils. New Phyt., vol. xviii, Nos. 3 
and 4, 1919. 
