470 
Copeland and Kalilenberg. 
In our exper iments, however, the injury to the roots was more 
likely to be due to the alkalinity than directly to the magnes¬ 
ium. The action of sulphur upon plants depends entirely upon 
the chemical combination in which it is present: sulphates are 
essential food, while sulphites and sulphides (usually, at least) 
are poisonous. 
According to Remsen, arsenic is not poisonous in the ele¬ 
mentary state, but becomes so when oxidized. And the violence 
of the toxicity depends further upon the degree of oxidation. 
Working with arsenites, Phillips (23) concludes that arsenic is 
more toxic than copper, and Nobbe, Baeseler, and Will (19), 
find that it surpasses zinc. On the other hand, working with 
arsenates Blake (1) finds that the toxicity depends upon the 
basic ion. Low (15) states that algae grow in 1 per cent, 
potassium arsenate: and Bouilhac (3) goes so far as to maintain 
that arsenates may replace phosphates in the nutrition of var¬ 
ious green and blue-green algae. This is denied by Stockiasa 
(28. Ref.) who places the concentration injurious to plants at 
N. N. 
As 2 0 3 and 1 AnA - As 2 Q 5 . Knop (10. Ref.) pronounces 
100,000 ' d 1,000 
arsenates harmless toward mature phanerogams. 
Manganese is injurious in the concentration used by Molisch 
(16) but it has been detected in the ash of a great number of 
plants. According to Spampani (26) while not a substitute for 
iron, it will postpone chlorosis. It is difficult to draw con¬ 
clusions from Stevens’ work (27) since in one table (p. 399) he 
rates the toxicity of KMn0 4 above that of potassium cyanide, 
sulphuric acid, or caustic potash, and in another (p. 401), de¬ 
clares that it is not poisonous. Stevens finds potassium chro¬ 
mate somewhat injurious to fungus spores, and potassium bichro¬ 
mate very much so. Knop (10. Ref.) agrees that chromic acid is 
injurious, but says that chromium oxide is without effect. The 
only statement with regard to tungsten is Knop‘s, that " Phos¬ 
phor wolf ramsaure” is fatal without being demonstrable in the 
ash. Cameron (4) regarded selenium as to some extent a sub¬ 
stitute for sulphur: but Knop (10. Ref.) and Bokorny (2) 
agree that, while telluric acid is harmless, the salts of both 
selenic and selenious acids are poisonous. Knop places boric 
