Stimulation of plants by carbon disulphide 
CARRIE OLDENBUSCH 
The problem of stimulation of plants by minute doses of 
chemicals, which are poisonous in higher concentrations, has 
long been an interesting one. Raulin (1) in 1869 was probably 
the first to undertake work of this kind, using a nutrient solution 
made up of a large number of substances as a culture medium. 
As the stimulant, Raulin added to his nutrient solution small 
amounts of metallic salts, such as silver nitrate, platinum di- 
chloride, or copper sulphate, and found that cultures of Asper- 
gillus niger, grown in these solutions produced a more luxuriant 
mycelium than cultures to which nothing had been added. 
Pfeffer (2) in 1895, by means of comprehensive experiments, de- 
termined that such a complicated nutrient solution was unnec- 
essary and originated a number of solutions which have been 
and are still extensively used in work of this kind. Benecke 
(3), in the same year, published a paper in which he also gave a 
much simpler normal solution than Raulin’s but slightly different 
from Pfeffer’s. 
Richards (4), using the latter’s solution with the addition 
of traces of zinc, iron, sodium, lithium, and other salts, obtained 
a heavier growth of Aspergillus niger and Penicillium glaucum 
than in cultures to which none of the above were added, demon- 
strating that Raulin’s solutions really resulted in stimulation. 
Ono in 1900 corroborated Richards’s results and also worked 
out the effect of these salts on certain algae. He found that 
algae as a rule have their point of greatest stimulation at a much 
lower concentration of the salt but in other respects are similar 
to fungi. Richards (5) and Ono (6) determined that the econ- 
omic coefficient of sugar is considerably lower in the cultures 
to which salts had been added than in the controls, proving that 
stimulated fungi require a smaller amount of carbohydrate 
food in proportion to the quantity of waste acid produced. 
Since this time many other investigators have worked on 
this problem, obtaining similar results. Kahlenberg and True 
(7) formulated a law which they gave as an explanation of this 
stimulation phenomenon. They claim that since the chemical 
and physical properties of solutions are due to the properties of 
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