THE KOOT. 99 



searching for it. The experiment of plantinnr a Strawberry in 

 a sandy soil, surrounded by rich earth, but not coniinir in con- 

 tact with it, when it was found that tlie roots immediately 

 sought the rich earth, was considered conclusive on this point. 

 But the explanation of this phenomenon is easy without having 

 recourse to any power or instinct on the part of the root for 

 seeking nourishment. The influence of the rich soil was felt 

 by the roots, although not in contact, and they became stimu- 

 lated by its action. There are other cases in which roots seem 

 to be endowed with the power of seeking nourishment. An 

 example is mentioned by Lord Kaimes of a Plane-tree stand- 

 ing upon a ruined wall in Ireland ; and when its nourishment 

 was exhausted, it sent down roots to' the earth, a distance of 

 ten feet, and continued its existence by this act, prompted, ap- 

 parently, by self-preservation. We have seen vines growing in 

 very rich moist soil send down roots four and five feet long to 

 the earth ; but in those cases it was at a curve downward of 

 the stem, so that the descending fluid must rise to reach the 

 roots. In all these cases we believe that it is the eftect of grav- 

 ity rather than of any voluntary or determining power of the 

 plant. In the corn, roots put forth from the lower nodes of the 

 stalk, and particularly in those that are luxuriant, and in seasons 

 of abundant moisture, — proving from their origin, and the cir- 

 cumstances under which they occur, that it is the accumulation 

 of descending sap that causes their development. All this is 

 purely the result of physical causes. It has been thought that 

 plants had the power of returning to the soil matters injurious 

 to them ; but this has been proved to be a simple result of 

 exosmosis, and that rotation of crops was not demanded to 

 avoid poisons eliminated by the plant, but from the fact of 

 certain necessary elements being exhausted from the soil. 



175. We have mentioned before that the root always de- 

 scends in its course of development, unless obstructed by phys- 

 ical impediments. Numerous experiments have been m.ide 

 which strikingly exhibit this vital impulse. To Dutrocliet, 

 more than to any other man, is the world indebted for ]>lacing 

 this subject in its present interesting position. In several 

 memoirs he has discussed the subject in its various connections, 

 and from his numerous experiments we arrive at the conclusion, 

 that quantitij of matter seems to exercise the most powerful in- 

 fluence in controlling the direction of the root. When the root 



What experiment with a strawberry? How explained? What case 

 montioned by Lord Kaiuies ? How explained? How do vines and corn 

 illustrate it? Have plants the power ot returning to the soil useless or in- 

 jurious materials? — 175. What controls the direction of tiie root? 



