118 NEW YORK STATE MUSEUM 



was, it is stated, largely the result of the efforts of Benjamin 

 Franklin, who is reported to have sown plaster on a clover field 

 near one of the principal roads in Pennsylvania in large letters 

 so as to form the sentence, " This has been plastered with 

 gypsum/' The clover which had been plastered was greener and 

 more thrifty than that which had not received an application of 

 the plaster, and the letters were distinctly visible at some dis- 

 tance. 



Probably the action of no fertilizer is so little understood as 

 is that of gypsum ; and those who have used it are in some cases 

 enthusiastic in its favor, while others are just as pronounced in 

 their opposition to its use. It is a question wheliier it has any 

 direct fertilizing value, though the ashes of nearly all the plants 

 contain varying percentages of lime and sulfuric acid which were 

 possibly derived from gypsum. Its value as a fertilizer is attrib- 

 uted by Liebig to its power of fixing ammonia from the atmos- 

 phere so as to make it available as plant food. 



It is the opinion of De Candolle that gypsum is a stimulant to 

 the leaves of plants; while Chaptel considered the stimulating 

 effect to be due to the saline character given to the sap of the 

 plants. 



Sir Humphrey Davy "regarded gypsum as a direct source of 

 plant food, because a certain percentage of sulfate of lime is 

 found in the ash of plants ; but the most satisfactory explanation 

 of its action is the theory advanced by Storer, which supposes a 

 threefold action, the first mechanical and the others chemical.^ 



1 The salts of lime have a tendency to flocculate loose soils, 

 making the soil more granular, while an opposite effect is 

 observed on clay soils where the soil is broken up into finer por- 

 tions. Gypsum as a salt of lime acts to a slight extent im this 

 way, but other lime compounds act much more rapidly. 



2 It is supposed that gypsum gives up part of its oxygen to 

 certain organic substances in the soil, thus preparing them for 

 plant food. 



* Storer. Chemistry of Agriculture. 1887. 1 :20<>-16. Quoted by Grims- 

 ley, Gypsum Deposits of Kansas, p. 132. 



