ROOTS AND THEIR FUNCTIONS. . 49 



suspended in the air, as well as those the roots of which 

 are buried in the soil. 



But there are many other important elements and 

 combinations, about which so little is known in regard 

 to their origin or action in the building of vegetable 

 structures that the most I need say about them is, that 

 they are important materials and should be supplied 

 whenever and wherever required. Among these are Sul- 

 phur, which is found most abundant in plants yielding 

 what are termed albuminoids. It is especially abundant 

 in plants of the Mustard Family, from the seeds of some 

 plants of which is expressed a valuable oil. It is also 

 abundant in Peas, Beans, Clover, and other seeds of leg- 

 umes. Sulphur is found in the form of sulphuric acid 

 combined as calcium sulphate or sulphate of lime, also 

 known as gypsum and plaster. Plants take up sulphur 

 in the form of soluble salts of sulphuric acid, but exactly 

 how these are utilized by them is not definitely known, 

 and it is perhaps for this reason that the use of gypsum 

 as a fertilizer for plants has so long remained a bone of 

 contention among agriculturists. Sometimes the results 

 obtained from an application of this material are seen in 

 a marked improvement in the growth of the plants, jbut 

 in other instances it has no apparent effect, and this, too, 

 on the same kinds of plants, and, so far as can be deter- 

 mined, on the same kind of soil. 



Iron js an indispensable element of all plants contain- 

 ing chlorophyll i. e., with green colored parts or organs. 

 It is, however, required in such small quantities that it 

 is readily obtained from the soil in all parts of the world. 

 Too much iron in the soil is injurious to plants, espec- 

 ially when in solutions that are readily absorbed and 

 distributed through the cells. 



Lime is an essential constituent of the ashes of plants, 

 and it is taken up as a sulphate of lime in such plants as 

 the Clovers, while in others, like Wheat, Rye, Oats, and 



