468 BROOKLYN BOTANIC GARDEN MEMOIRS 
RESPONSE OF Roots TO CONTACT STIMULATION 
Excelsior 
In the experiments so far enumerated no account has been taken 
as to the effects which various substances coming in contact with 
stems may have upon the growth of roots and other organs. It is 
quite natural to expect that if one organ is affected by a stimulus 
other organs will be, inasmuch as the organism as a whole responds 
to stimuli of quite insignificant character. Incidentally, we observed 
in our early experiments with seedlings grown in sawdust that the 
roots in some cases respond when the serial portions of the plant were 
in contact with excelsior. In 1912 experiments were carried on for 
the purpose of comparing the growth of roots in soil under different 
conditions. These experiments consisted in the growing of roots in 
boxes with glass sides. In one series the roots were grown in holes 
or channels along the edge of the glass, and in the other series no 
holes were provided. In both series there would be contact, but 
where the roots followed the channels, there was less contact of the 
roots with the soil particles than where they had to force themselves 
through the soil. These experiments being limited, however, did not 
furnish data of any particular value, although from the more or less 
meager data obtained, they seemed to indicate that the presence of 
grooves or channels in the soil produces less stimulating effect on the 
growth of roots than when more thorough contact exists. Most of 
our investigations relating to the effects of contact on roots were 
made with excelsior, and in some cases sphagnum moss and cocoa 
fibers were used. In many experiments we have also utilized various- 
sized particles of gravel, sand, and silt suspended in water. The 
excelsior which we employed did not produce any bad effect on the 
growth of roots when submerged in water. On the other hand it 
appeared to clear up the water in some instances, inasmuch as it 
was apparent that it absorbed certain accumulated products which 
sometimes occurred, and which were more or less detrimental to the 
growth of the roots. The water containing the excelsior cultures 
was clearer and possessed a more agreeable odor than those cultures 
where it was not used. As the seeds were suspended over water on a 
fine-mesh cotton cloth netting, these would occasionally become too 
moist and in this way the water became more or less turbid, owing to 
the presence of various extract substances derived from the same. 
The presence of excelsior in the water had a tendency to prevent any 
abnormality in the growth of the roots which might follow from the 
presence of foreign substances, and in this respect it acted like sand 
and charcoal in removing certain impurities such as copper sulphate. 
