1907] JENSEN—TOXIC LIMITS AND STIMULATION 13 
(34) says that 62/ to 12n/1oocco and ONo (32) that 25n/ to 
20on/toc000 ~produce the greatest dry weight of mycelium in 
Aspergillus. RicHTER (35) did not get acceleration of growth with 
CuSO, nor with AgCl. 
Within the past decade considerable work on seedlings of higher 
plants dealing with their relation to toxic agents has appeared. 
In nearly all cases this work has been limited to the effect of the 
toxic agent upon some particular part or organ, and has taken no 
account of the endurance of the plant as a whole for the poison. 
Thus KAHLENBERG and TRUE (21) record a large number of experi- 
ments upon white lupine radicles. They determined for this organ 
the fatal dose of various organic and inorganic substances. They 
found that H and OH ions are the deleterious agents. This work 
establishes the limit of endurance of the root-tip of white lupine 
only, and not, as Couprn (10) points out, the endurance of the 
whole plant. In the same fashion HEatp (19) worked with seed- 
lings of Zea, Pisum, and Cucurbita. He found that in KCN, K,Fe 
(CN)., and K,Fe (CN), the electro-negative ion or anion was toxic. 
In all others it was the electro-positive ion or cation. PLOwMAN (33) 
dealt with the question from the standpoiat of electricity and mag- 
netism. From the fact that plants in the soil in the vicinity of the 
positive pole were stimulated, while those at the negative pole were 
not, he concluded that ionization of the soil solutions bore directly 
upon growth. 
That roots may accommodate themselves to gradually increasing 
concentrations of toxic substances (38) has long been known, as 
has also the fact that the power of absorbing water containing salt 
is lost more and more by roots (36) the longer they are in contact 
with it. GuTHrm and Heros (16) worked with wheat, maize, 
barley, and rye in pot cultures, using native soil. Their idea was 
to determine the endurance of some farm crops for certain injurious 
Substances frequently present in soils. Table A, made from their 
data, shows the per cent. of poison which prevents germination. 
From these results it would seem that seeds will successfully ger- 
Mminate in somewhat higher concentration than that in which the 
Plants will later grow. True and OGLEVEE (42) found that various 
insoluble substances, potato starch, paraffin, coal, glass, filter paper, 
