1890-91.] Dr Murray and Mr Irvine on Silica in Seas. 
245 
and transferred to a fresh portion of culture solution pure and 
simple. For a time the plants continued to live, but their increase 
was trifling, and after twenty-seven days they presented the appear- 
ance of dead organisms, being deprived of their green colour, ceasing 
to give off oxygen in sunlight, and were without motion. 
(C) Another patch of (A) carefully washed was placed in cul- 
ture solution, into which a quantity of very finely-levigated clay 
from the fields was introduced. (This clay by careful washing was 
entirely freed from any soluble matter.) After a short time the 
whole clayey matter became entirely altered in appearance, forming 
a sticky matted-like substance, from which in sunlight oxygen was 
freely given off, and which under the microscope showed an 
enormous growth of Diatoms, having the characteristic yellow- 
green colour of the healthy algse. This experiment has been 
continued for a number of months, and the results obtained, so 
far as the development of Diatoms is concerned, has been so 
extraordinary that we have examined with the utmost care any 
possible source from which they might derive silica (apparently 
necessary to their life functions), other than from the clay which 
was added.* 
The experiment (B) seemed to prove conclusively enough that 
siliceous plants cannot obtain silica in sufficient quantity from the 
glass vessels used for that experiment. We were also suspicious 
that atmospheric dust might have provided a certain amount of 
siliceous nourishment, but the fact that the Diatoms in experiment(B) 
had been unable to live seemed to us to prove that neither from the 
glass vessels nor from atmospheric dust could they obtain, under the 
* Johann Nave, writing of Diatoms, remarks that these Algse abound 
wherever water collects, from the sea to the smallest puddle on the way- 
side, and are generally associated with clay or mud. Gerstenbergh’s plan 
for the propagation of Diatoms is instructive. He spreads the mud (containing 
Diatoms) on a plate or shallow dish, and exposes it to the full light of the sun. 
Stimulated by its rays, the plants begin to multiply rapidly, and on removal 
those left in the mud may be stimulated into active production by repeating 
the same process. By degrees the vitality of the little plant exhausts itself, 
and it is necessary to revive their vegetative powers. This may be accom- 
plished by creating an artificial spring and winter. You have only to allow 
the water to evaporate, and the mud to become nearly, but not quite, dry, when, 
on fresh water being poured over it, vegetation commences anew. In this 
way gatherings originally poor may be made to yield an abundant supply of 
Diatomacea. 
VOL. XVIII. 
20/5/91 
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