PURE CEOP OP TJNIPOEM AGE. 17 



their roots, (iii) by eroding the soil round their roots and thus leav- 

 ing these exposed, (iv) by partially or completely submerging 

 their crowns, (v) by rendering the soil too wet, (yi) by depositing 

 round their roots soluble saline matters in quantities large enough 

 to thicken the moisture in the soil to such an extent as not only to 

 prevent any further absorption by the roots, but even to set in 

 movement a contrary current of endosmose from the plants into the 

 soil, (vii) by introducing or increasing the quantity of poisonous 

 matters in the soil, (viii) by leaving behind a deposit of silt, which 

 may raise the level of the soil too suddenly, thereby injuring th^ 

 roots owing to insufficient aeration ; and (ix) by clogging the assi- 

 milating surfaces of the plants with a thick opaque layer of mud. 

 In the present case we are concerned chiefly with the first five 

 modes of injury, as the rest must affect more or less equally all 

 plants of the crop. Moreover the fourth and fifth modes of action 

 have Uttle or no effect on certain species, such as sissu, tamarifek' 

 sundri, &c. The stronger and larger and better-rooted plants will of 

 course generally have the advantage, but a violent rush of water 

 might lay down the large and vigorous tree or at least strain and 

 injure its roots, while its weaker neighbour, owing to the very 

 fact that it opposes slighter resistance, might be merely bent down 

 for the moment, to rise up again as soon as the flood has subsid- 

 ed and then shoot up ahead of it. 



Besides affecting the growth and stability of plants, floods may 

 also wash away or bring in seeds, as well as influence, favourably 

 or unfavourably according to the species concerned, their germina- 

 tion. 



(f) Action of man.— The action of man is all powerful in the 

 struggle for existence. 



If he is simply bent on satisfying his own immediate wants, he 

 cuts out only what suits him, and he takes it out in the easiest and 

 least expensive manner for himself. The relative size and vigour 

 oT the trees does not concern him in the least ; he will often cHmb 

 Tip into a tree to cut out only the portion of it that suits his pur- 

 pose. The effect of his action on the growth of the surrounding or 

 overtopping trees is no business of his. 



If he is interested in working out the trees with the greatest ad- 

 vantage to himself as well as to the forest, his action will be direct- 

 ed to modifying in the most favourable'manner the'natural struggle 

 for existence. Here he will remove or keep back the larger plant 

 to encourage its weaker neighbours ; there he will fell the smaller 

 one in order to give more growing room to the larger and more 



