258 STATE BOAED OF AGEICULTUEE. 



Lime 33 



Sulphuric acid 46 



Water 31 



Total 100 



If plaster is heated for some time to 400"^ it lo?cs its water of hydration, and 

 then becomes "boiled plaster" or stucco, having the power to again combine 

 with water when mixed up with it, and setting in a mass nearly as hard as the 

 original stone from which it was formed. It is sparingly soluble in water, one 

 part of gypsum dissolving in 500 parts of water. Water holding this substance 

 in solution is " hard," and unfit for most domestic uses. 



Gypsum is sometimes found of a very compact structure, and partially trans- 

 parent. It is then known as alabaster, and is much used for ornamental pur- 

 poses. It is sometimes found perfectly crystalized and transparent like glass, 

 and is then called selenitc. But its composition in these various forms is still 

 the same as the material we grind up for plaster. 



INFLUENCE ON PLANTS. 



The most marked influence of plaster on plants is a large increase in the 

 formation of leaf and stalk, as distinguished from the formation of seed ; at the 

 same time it imparts a dark green color to the leaves of the plant, giving an 

 impression of very vigorous growth. It is also found to impart a peculiar ten- 

 dency to the development of leaves in a plant, so that it not only develops leafy 

 plants, but the leafy parts of plants. The plants which are especially benefited 

 by plaster are usually those of a very rapid growth : i. e., plants which naturally 

 complete their growth in a comparatively short period of time. 



This increased vigor of groAvth, the larger stem, more numerous leaves, and 

 especially the rich green color of the leaves, makes the farmer feel certain that 

 the 2)laster has greatly benefited his crops. He needs no better evidence, for he 

 can see the improvement, and seeing is believing. This would be satisfactory if 

 the herbaceous part of the plant constituted its chief value. But if it is some 

 other part which is chiefly valuable, — the grain instead of the straw — and if the 

 plaster has simply increased the straw, without a corresponding increase of grain, 

 the farmer may be greatly misled by judging of the effects of plaster simply by 

 the looks of his crops. 



Plants manured by plaster are also said to form a larger proportion of the 

 highly organized products of plant life. Professor Storer, in a late Bulletin of 

 the Bussey Institution, p. 37G, says : "Analysis has shown that plants manured 

 with gypsum or with Ej)Som salt are often richer in nitrogenous constituents 

 than those grown upon adjacent land that had not been manured." It would 

 seem thus to contribute especially to the development of those constituents of 

 the plant which go to build up the muscular tissues of the animal and give him 

 power of endurance : which make him strong rather than fat. 



KINDS OF PLANTS BENEFITED. 



We now enter upon a topic concerning which there has been a great diversity 

 of views. On such a subject the first and most important appeal is to the expe- 

 rience of farmers. We must first ascertain the facts, and then cxjjlain these 

 facts by general laws if we can ; but it is not safe to frame the law first, and 

 then decide by this what the facts should be. 



Boussingault gives a summary of a very valuable report made to the Eoyal 



