CHEMOTROPISM OF ROOTS." 
FREDERICK C. NEWCOMBE and ANNA L. RHODES, 
THE chemotropism of pollen tubes and of fungus hyphae 
and the chemotaxis of various unicellular organisms have received 
considerable attention in the great mass of work which has 
been done on the sensitive activities of plants. There is probably 
a well-defined notion that terrestrial roots, which are known to 
be hydrotropic, are also chemotropic. The unequal distribution 
of minerals in the soil, and of decaying organic matter, can be 
thought of as furnishing opportunity for the development of 
chemical response as a biological adaptation. 
In literature there seems to be no record of work done to test 
the ability of roots to respond to a chemical stimulus by changing 
their direction of growth. This test has now been made, and 
the results are recorded in the following pages. : 
I. THE ONE-SIDED APPLICATION OF CHEMICALS IN TUBES, 
The first method employed consisted in applying to the tips 
of roots immersed in a liquid a chemical diffusing from the open 
mouth of a horizontal tube. 
A considerable quantity of the ordinary Sachs’s culture fluid 
was made, containing all the ingredients except the potassium 
nitrate. A solution of potassium nitrate was then made of such 
a density that when a drop of it was placed in the solution of . 
the other ingredients of the culture fluid, the potassium nitrate 
would neither rise nor fall. Rather large capillary tubes were 
now made, 1.5°™ long by 1™™ internal diameter and closed at one 
end. These tubes were then filled with the solution of potassium 
nitrate by the use of the air pump. Next, a row of seedlings, 
fastened by strips of blotting paper and rubber bands to a bar of 
glass, were suspended across a glass cylinder, the roots being 
immersed in the culture fluid containing no potassium nitrate. 
The tubes filled with the potassium nitrate solution were now 
introduced into the jar of liquid, and so adjusted that their open 
*Contribution 68 from the Botanical Laboratory of the University of Michigan. 
1904] 23 
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