26o 
R. H. TRUE AND H. H. BARTLETT 
loose relation existed between the length of the first internode and the 
length of the hypocotyl on the one hand, and either the development 
of the root system or composition of the medium, on the other. A 
much closer relation seemed to hold between the length of the primary 
root and the composition of the medium; consequently, in this paper 
the length of the primary root only is correlated with the chemical and 
physical data. 
Throughout this paper concentrations are expressed as multiples 
o( M X io~^. M has its usual significance; it indicates a solution 
containing the gram-molecular weight of a compound in one liter of 
water. A solution whose concentration is ikf X io~^ is therefore of 
one one-millionth molecular concentration, and a solution ten times 
as strong, for example, has the concentration loM X io~^. In our 
work the least difference in concentration between adjacent cultures 
of a series containing only univalent ions was 6M X io~^; the greatest 
was s^M X lo-^ 
The reader will of course understand that two solutions of the 
same gram-molecular concentration are not necessarily chemically 
equivalent. A molecular solution of Ca(N03)2, for example, is elec- 
trolytically equivalent to a twice molecular KNO3 solution. This 
fact should be kept constantly in mind in order to avoid confusion in 
comparing the curves for the different experiments. It will be noticed 
that the distilled water curve is much flatter in the case of the bivalent 
salts than in the case of the univalent salts. This is due to the fact 
that the concentration of electrolytes excreted by the roots is in the 
one case expressed in terms of a bivalent salt, in the other case in terms 
of a univalent salt. In the case of all the univalent salts which we 
used except KH2PO4, the conductance of equimolecular solutions was 
about the same for all, and roughly half the conductance of the bivalent 
salts. KH2PO4 is exceptional, as may be seen from the curves. It 
dissociates for the most part as a univalent salt into K+ and H2P04~ 
ions, but has a much lower conductance than other univalent salts. 
The curves are therefore very steep in the figures which deal with 
KH2PO4, and in view of the fact that this salt induced excretion, the 
shape of the curves can not be regarded as very significant. 
There is no reason to doubt that absorption and excretion of 
electrolytes take place simultaneously in all culture solutions. The 
figures accompanying this paper indicate of course only the net result 
of the two processes at any particular time. It would be very desir- 
