ROOT ABSORPTION 



159 



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 

 FIG. 139. Water cultures rooted in the soil. For some plants the 

 of Buckwheat, showing ef- water culture gives good results, when 

 feet of the lack of the dif- the galtg are in guch ft proport i on that 

 ferent mineral elements: rt ,.. ,. A , , 



1, with all the elements; 2 llterS f . the S lu - 



2, without potassium; 3, tion contain 1 gram 

 with soda instead of potash; of potassium nitrate, 

 4, without calcium; 5, with- i gram of iron phos- 



ammonia P hate > i S ram of cal - 

 cium sulfate, and ^ 



gram of magnesium sulfate. The results of 

 omitting some of these salts are shown in 

 Figure 139. 



Root Absorption. For the process of os- 

 mosis upon which the entrance of water into 



the root depends, the epidermal cells of the p IG> 149. Root 



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

 the root hairs they have a large surface in l a y er of protoplasm 

 contact with the soil solution. Having thin and lar s e vacuole. 

 cellulose walls against which their protoplasm 

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

 of water into their large vacuoles. (Fig. 140.) As the student 

 already knows from his acquaintance with osmosis, the entrance 

 of water into the epidermal cell depends upon the concentration 



