ROOT ABSORPTION 



169 



Each of the mineral salts which plants require, apparently, 

 is so specially related to the nutrition of the plant, that not one 

 of them can be omitted, although all others are present in 



suitable quantities. This fact is dem- 

 onstrated by growing plants with their 

 roots in distilled water to which the dif- 

 ferent mineral salts can be added in such 

 proportions as the experiment demands. 

 When the salts are added in such pro- 

 portions that the solution imitates a soil 

 solution, such as ordinary spring or well 

 water, many herbaceous plants are able 

 to grow in it till they have flowered and 

 produced seed. In fact, aside from the 

 lack of anchorage and having to supply 

 their roots with oxygen from the shoot, 

 plants may do almost as well as when 

 rooted in the soil. For some plants the 

 water culture gives good results, when 

 the salts are in such a proportion that 

 2 liters of the solu- 

 tion contain 1 gram 

 of potassium nitrate, 

 ^ gram of iron phos- 

 phate, 5 gram of cal- 

 cium sulfate, and J 

 gram of- magnesium sulfate. The results of 

 omitting some of these salts are shown in 

 Figure 1S9. 



Root Absorption. — For the process of os- 

 mosis upon which the entrance of water into 

 the root depends, the epidermal cells of the fiq. 140. — Root 

 root tip are especially fitted. By means of hair showing the thin 

 the root hairs they have a large surface in layer of protoplasm 



contact with the soil solution. Having thin ^f ^^'^l ^^^^^^^- 



, , . ^ ■, Alter rrank. 



cellulose walls against which their protoplasm 



is spread out into a thin hning, root hairs afford an easy entrance 



of water into their large vacuoles. {Fig. I40.) As the student 



already knows from his acquaintance with osmosis, the entrance 



of water into the epidermal ceil depends upon the concentration 



Fig. 139. — Water cultures 

 of Buckwheat, showing ef- 

 fect of the lack of the dif- 

 ferent mineral elements: 



1, with all the elements; 



2, without potassium; 3, 

 with soda instead of potash; 

 4, without calcium; 5, with- 

 out nitrates or ammonia 

 salts. 



