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activities of the plants. So far as we can see now, the development of the plant, its 
functional activity, is not dependent upon the quantity of plant food in solution, hut 
upon the character of the plant food. Plants will grow as well — that is, have the 
same functional activities -in a soil solution which has a resistance of ."),()()() ohms in 
our electrolytic cell as they will in the culture solution made up of these different 
salts with a resistance in our cell of 250 ohms; that is, there is ten or fifteen times as 
much plant food in one as in the other, and yet there is no apparent difference in the 
development of the plant, no apparent difference in the functional activities of the 
plant, It breathes as well, it feeds as well from these dilute as from the more con- 
centrated solutions; hut when we put a trace of lime or a trace of manure extract or 
a trace of some of the salts that are used in fertilizer work or ordinarily applied to 
the soil, to either the stronger or more dilute culture solution, we may change, to a 
marked degree, the functional activities of the plant and make it altogether a different 
soil or a different solution as regards the growth or development of the crop. 
Our experience, since Bulletin 22 was issued, indicates very clearly that the amount 
of plant food in solution does not affect the character of the crop within very wide 
limits, hut that the character of the salt in this solution, or the character of the salt 
added to the solution, has an important and remarkable effect in many cases on the 
development of the plant. It seems as though the potash salts were not needed by 
the plant as an additional^ source of food. You can safelv Use potassium chlorid or 
potassium nitrate or potassium phosphate or potassium sulphate, although they appear 
to have somewhat differenteffectson plants— possibly have different effects on different 
plants. We have not gone far enough to determine this definitely. But when you 
add the other potash salts, such as potassium chlorate, which has potash and chlo- 
rin associated with oxygen, you get an entirely different effect, and it can not be 
substituted at all for potassium chlorid. You have the potash and the chlorin, but 
the potassium chlorate has different properties as a salt from potassium chlorid, and 
it is unquestionably a fact that the influence of these salts is felt not only through the 
ions, but through the undissociated portion of the salt, if there be any present. In 
this respect it is quite analagous to the effect of salts on the human system. We take 
sodium chlorid as a necessary salt to aid digestion. You can not successfully sub- 
stitute ammonium chlorid, still less could you substitute potassium chlorate as a 
source of chlorin. One combination of mercury and chlorin is used as a medicine; 
another combination is deadly poison to the system; both contain mercury; both 
have chlorin; it is not in any one of these but in the combination that the effect is 
felt. So it seems to be in the case of the plant. Potassium sulphate may be health- 
ful; it may prevent the plant from corking up; it may protect it from the irritating 
condition of the soil. How it is accomplished I do not know, but I have seen the 
effect. Potassium chromate will cause the plant to cork up very quickly, and will 
check the transpiration so rapidly and completely that the plant can not adjust itself 
to its conditions and live, so the plant dies. 
Another very interesting thing — a very significant thing — that has developed is 
that, if the plants are growing with their roots freely exposed to the moist air above 
the culture solution or to the moist air at the side of the soils, these deleterious influ- 
ences that seem to exist in the poor soils do not affect them appreciably. In some 
of our earlier experiments plants were grown in about 400 grams of soil in glass 
tumblers. The transpiration was measured, but we got no differences from different 
soils compared with what we got in larger pots. After a great deal of work and a 
great many experiments had been tried we found that the roots were confined almost 
entirely to the air space between the soil and the glass formed by the contraction of 
the soil. The roots formed a network around the soil. They were not actually 
growing in the soil, but half in and half out of the soil, and the development of the 
hair roots was most marked. They looked like plumes. Even after weeks of 
growth they showed none of the characteristics of plants growing in the larger 
masses of soils or in the soil solutions. Then an attempt was made to see if in the 
culture solution prepared from the soils, with an equal amount of aeration as in the 
tumblers, these differences in the different soil solutions would disappear, and the evi- 
dence is that they do disappear. That is, if you let the solution trickle down the 
roots, or if you give the plant an intermittent watering; or, if they are put in test 
tubes and the water allowed to drop slowly upon them and arrange that the tube 
when filled be automatically emptied by a siphon, leaving the roots exposed for a 
time, these differences disappear; we get normal roots in solutions which when 
grown without that treatment give us a root system that is corked up and undeveloped 
and impossible of further development, It would seem, therefore, that our position 
in Bulletin 22 in that respect is confirmed — that the use of fertilizers, at least some- 
times, appears to have the same effect as good cultivation, and it appears now that 
if we have perfect aeration, such as we get in a small volume of soil, and conditions 
where the root can grow half in the soil and half in the air, these differences disap- 
