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 afTected 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 gfown 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. 



