24 ELEVENTH REPORT. 



MUTUAL INTERACTION OF PLANT ROOTS. 



J. B. Daxdeno. 



The experiments here described are a continuation of certain laboratory 

 cultures made during 1907 and previously, and published in the tenth report 

 of the Michigan Academy of Science. These experiments are also in a sense 

 preliminary to a further investigation along the same line, having as the 

 chief aim in view the study of the effects of the roots of certain economic 

 plants the one upon the other. In dealing with such a matter as this, where 

 there may be such a variety of influences and conditions, it is advisable to 

 experiment very extensively and to be cautious and conservative about 

 conclusions and theories relating to them. These experiments are, therefore, 

 by no means considered conclusive; and the results are here published simply 

 as so much further data relating to the one subject indicated in the title al:)ove. 



Several years ago when working on a farm, one of the common jobs during 

 the month of June was cutting Canada thistles in the grain fields before the 

 grain had headed out, and at a time when the thistles were taller than the 

 grain. At this time it was frequently observed that the })atches of thistles 

 were growing in the best patches of grain. No explanation was ever offered 

 for this seemingly peculiar phenomenon excepting that it was thought thistles 

 would not grow on the poorer land, consequently they were found only on 

 the most fertile portions of the field. In these fertile spots the grain crop, 

 would, of course, be expected to surpass the rest. But these explanations 

 never seemed satisfactory. 



Certain results of experiments with pairs of plants growing in the labora- 

 tory in water cultures seemed to point towards a partial explanation of this 

 peculiar condition, and as a result of this hint, a series of experiments was 

 planned to see if any light could be thrown u])on this matter l^y exi^erimenting 

 with pairs of plants in pots. Incidentally it might be mentioned here that 

 the Canada thistles do not reproduce by seed to any very great extent, and 

 not by any means so extensively as is commonly supposed. They reproduce 

 by underground stems which sometimes extend out through a radius of four 

 or five feet in one season. This underground system of the Canada thistle 

 is often very deep and extensive and the suggestion arises as to the effect 

 it might have upon the soil and directly or indirectly on the other plants 

 growing in the same soil. 



It is a well known fact among farmers that the thistle patches in the field 

 persist as patches for many years, spreading if neglected, but holding their 

 own generally when once they gained a deep foothold. Such patches then 

 might be supposed to exert some kind of influence upon the soil from con- 

 tinued occupation of the ground by thistles. 



The experiments here described were planned to show whether the under- 

 ground system of the thistle did affect the crop growing in its neighborhood. 



Flower pots, some 4-inch and some 6-inch were sunken into the ground 

 and then fitted with a well mixed rather poor sandy loam soil. It was not 

 deemed necessary at this stage to pay much attention to the chemical con- 

 dition of the soil, supposing that for practical purposes the main thing was 

 to have the soil all alike and well mixed. 



When the soil and pots were all prepared four 4-inch j^ots and four 6-inch 



