Metals and Plants. 
469 
fuse readily in to the interior of the roots, is shown by their 
staying alive and attempting to form lateral branches; as was 
noticed again in the case of manganese. In minute quantities 
iron is a necessary plant food. Ferrous salts may be injurious 
chiefly by their reducing action. Richards finds Fe S0 4 in ap¬ 
propriate dilution to act as a stimulant upon aspergillus. Kah- 
lenberg and True place the concentration at which Fe ions exert 
N 
a fatal influence at less than — 
The same authors give the greatest concentration at which 
lupines can endure cadmium salts as 
N 
204,800 showin S that these 
salts are exceedingly toxic. Guenther finds cadmium more 
poisonous than zinc for fungi. Blake (1) from experiments 
upon animals cites cadmium and thallium as typical elements 
of high atomic weight and intense physiological action. Knop 
finds thallium, like gold and silver, deadly without being 
demonstrable in the ash. Both thallium and cadmium made 
short work of our plants. 
The literature upon zinc as a poison is very extensive, but 
wanting in quantitative data. Knop (11) attempted to sub¬ 
stitute it for calcium, and found it injurious when present as a 
trace in the roots. Molisch and Gunther agree that it is 
poisonous. Nobbe, Baeseler, and Will (19) find it more pois¬ 
onous than lead but less so than arsenic (as arsenite). Kranch 
(12. p. 282) finds it injurious in minute quantity in water 
cultures, but less so in the ground, which experiment would 
undoubtedly show to be true of other poisons. At a sufficient 
dilution it acts as a stimulant. The toxicity of lead is likewise 
generally recognized, but without there having been any 
quantitative determinations it is probably less intense than 
that of many other metals. 
We know no previous work upon the effect of antimony upon 
plants, but its salts have a more intense action in animal 
physiology than do those of bismuth. Bismuthyl phosphate is 
not immediately fatal to corn (10. Ref.). 
While magnesium is a necessary food of all plants, it is not 
improbable that it may under some conditions act as a poison. 
