54 RELATION OF ROOT TO SOIL 



sible that we may have a new explanation for the sterile condition 

 of some soils; also plowing and the use of fertilizers may have a 

 new meaning. Consequently when a potted plant shows signs 

 of starvation it is removed from the jar, the tangled mass of roots 

 next to the jar is cut off together with a portion of the earth and 

 then repotted with fresh earth. In this way room is given for 

 the rootlets to grow out into the earth and develop a new ab- 

 sorbing surface and additional materials are placed at the disposal 

 of the root. This relation of the root hairs to the soil particles 

 explains to us why transplanted seedlings usually wilt. Many 

 of the root hairs have been killed and the seedling does not revive 

 until new root hairs have been developed. So also it is clear 

 why most shrubs and trees should be transplanted in September 

 or October or in the early spring in order to permit the rootlets 

 which renew their growth very early in the spring to establish 

 in the soil new absorbing surfaces before the leaves develop and 

 bring about an excessive loss of water through transpiration. 

 Why are plants often pruned or cut back in transplanting? 

 Why is nursery stock frequently transplanted, generally a year 

 before it is to be permanently planted? 



You have often noticed that fields of grain and other crops turn 

 yellow and die during a long rainy season. This is due to the 

 fact that the air spaces between the earth particles become filled 

 ■with water and there is no longer possible an interchange of gases. 

 At least two-fifths of the space in these capillary pores should be 

 filled with air to insure healthy plants. This is particularly 

 noticeable in clay soils which are referred to as cold, wet, and 

 sour soils. The reason of this is that the earth particles of such 

 soils are very fine and, owing to their enormous surface, they 

 hold the water with great tenacity. In this way acids from 

 decaying vegetation as well as other substances accumulate in 

 excess and render the soil unwholesome. Therefore heavy clay 

 soils, which are richer in plant foods than other soils, require an 

 admixture of sand and an adequate drainage to render them 

 sufficiently porous for a proper circulation of air. Sandy soils 

 are made of coarser particles and therefore looser. For this 

 reason the capillary water is not retained for any considerable 



