140 Food from the Soil 



large quantities of iodine, which, like the rest of their 

 food, they draw from the sea. With the smell of 

 iodine we are all no doubt familiar ; but if we mix one 

 part of iodine with 300,000 parts of water we entirely 

 lose it. That is to say, no one of our senses is keen 

 enough to detect it. We can neither see, nor taste, 

 nor smell it. But of course it is there, and we can 

 find it again by adding starch, which is turned to a 

 brilliant blue by coming in contact with even this 

 minute quantity. 



But the iodine contained in sea-water is less even 

 than this — it is less even than the hundredth part of 

 this infinitesimal amount. And yet the sea-weed 

 manages to extract it. And although plants take their 

 mineral food in such weak dilutions that we cannot 

 detect its presence either by taste or smell, and might 

 be inclined to think that it can matter very little what 

 it is, yet they are discriminating ; and their roots have 

 to some extent the power of choosing what they will, 

 or will not, take up. 



This is evident from the fact that plants growing 

 side by side will take up different food, or take it in 

 very different proportions. 



There is, for instance, the common reed and the 

 common species of moss, which both grow in b.ogs. 

 The soil is dissolved by water and gases equally for 

 both, and both take up a good deal of dissolved flint, 

 or silica; but the reed takes up also a very small 

 quantity of salt, a little more, but still a very small 

 quantity, of iron, no soda, a little magnesia, and a great 

 deal of phosphoric acid ; whereas the moss, which grows 

 close by, takes very little either of phosphoric acid, 

 magnesia or salt, but some soda, and much iron 



