108 ~ TUE ROOT. 



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 seat down roots to the earth, a distance of 

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

 apparently, by self preservation. We have seen vines grow- 

 ing in very rich, moist soil send down roots four and five feet 

 lonjj to the earth ; but in those cases it Vv^as at a curve down- 

 wards of the stem, so that the descending fluid must rise to 

 reach the roots. In all these cases we believe that it is the 

 effect ofgr-vity opposed to vital action, rather than to any 

 voluntary or determining power of the plant. In the corn we 

 see roots put forth from the lower nodes of the stalk, and par- 

 ticularly in those that are luxuriant, and in seasons of abun- 

 dant moisture, proving from their origin and the circumstances 

 under which they occur, that it is the accumulation of de- 

 scending sap that causes their. development. 



132. Although roots do not possess the power of selecting 

 their appropriate nourishment, or rejecting what is deleterious, 

 yet they have the power of returning to the soil the noxious in- 

 gredients which they absorb. This is shown by an experiment 

 of Macaire recorded by several Botanists, of a plant having half 

 its roots immersed in a jar containing a solution of acetate of 

 lead, and the other half of the roots in one containing pure 

 water ; in a short time acetate of lead was found in the jar of 

 pure water, showing that the plant had taken the lead into its 

 system, but had thrown it off again, as unfit for assimilation. 

 It has long been known that roots give off peculiar substan- 

 ces, but it has not till recently been considered a universal 

 and necessary function of plants. There is no doubt, that it is 

 as necessary to the healthy action of the various vegetable 

 organs that the deleterious matters, or such as are unfit for 

 the particular species, should be ejected from the system, as 

 that excrementitious matter should be voided by animals. 



133. It has long heen known to agriculturalists, that the same 

 crop will not flourish on the same ground for many years in 

 succession : hence tiiey adopt the rotation of crops. The 

 above princi])le is a plain reason why this is the rase. Wheat 

 for instance produces an exudation from its roots which is de- 

 leterious to this phmt, and if wheat be sown year after year 

 on the same soil it becomes impregnated with a substance inju- 

 rious to wheat, and the proper nutriment becomes exhausted. 

 This excretion of wheat may be appropriate food for cotton 

 or tobacco, and of course these crops may flourish where 



