54 Fruit-growing in Arid Regions 



and the amount of water and of raw food materials. 

 Ordinarily roots should penetrate deeply in mountain 

 soils for the reason that orchard land is, or should be, 

 deep and with no hard subsoil. But if the soil is shallow, 

 or the moisture and supply of food materials are largely 

 near the surface, the roots soon occupy the space in spite 

 of the fact that it is their nature at first to grow down- 

 ward. Those instances in which roots, when very young, 

 grow upward, are very likely due to poor cultivation and 

 the consequent location of the food materials and moisture 

 supply near the surface. Eventually, however, the upper 

 layers of soil are largely occupied with a mass of small 

 roots. 



Roots may grow to great lengths in poor soil, but in a 

 fertile soil they tend to make shorter growths and to 

 occupy all of the ground. A root of a cottonwood tree 

 recently brought to the writer was forty-eight feet in 

 length and only one and one-half inches in diameter at the 

 larger end. This tree grew in the mountains in a rocky 

 situation near a river bank. The root pushed out laterally 

 just beneath the surface, evidently in search of water, 

 till finally a change in the river bed caused it to be washed 

 out. 



All of the elements of plant-food, with the single excep- 

 tion of carbon, are taken into the plant from the soil in 

 solution. The larger roots are not concerned to any great 

 extent in this process of absorption, but near the end of the 

 smallest growing points are the regions where this process 

 takes place. Just back of the growing tip is a short zone 

 where minute and often invisible growths, known as 

 root-hairs, push out from the outer cells. These root-hairs 



