Ill] ROOT RANGE 35 



present. These various relationships have already 

 been discussed at some length: we need now only 

 point out that a water supply suitable for ordinary 

 plant growth seems also to be very suitable for 

 bacterial activity. The rule seems to apply also to 

 other soil conditions, and we may make the general 

 statement that a soil suited to the growth of plants 

 is also suited to the activity of bacteria and there- 

 fore to the production of plant food. The similarity 

 becomes even more close after the soil has been 

 partially sterilised so as to destroy detrimental 

 organisms. 



A further connection between the food supply and 

 the water supply lies in the fact that the food has 

 first to be dissolved in the soil water before it can 

 enter the plant. Roots have no power of taking in 

 solid matter ; they can only imbibe solutions ; further, 

 they cannot use strong solutions, but may even be 

 injured thereby as in some of the alkali lands; and 

 they do not make very good growth in too weak 

 solutions. 



Even this is not all. The amount of plant food 

 per unit volume of the soil is not the only factor 

 determining the amount of food the plant can get; 

 the extent of the root range is equally important just 

 as it was in the case of water. 



Root range. And this leads to the question of 

 root room. No plant does well unless it has ample 



3—2 



