FARM EXPERIENCE. " 237 



correctives on that point. That was one reason why I brought 

 the matter before this meeting. The grasses I have generally 

 got rather heavier after turnips, after the second year. 



Prof. Johnson. There seems to be a question here in re 

 gard to the action of plaster. All these plants of the radish 

 and turnip family contain a volatile oil. You know that the 

 turnip plant itself has an odor which is due to the presence 

 of the volatile oil. In the case of the horse radish and simi- 

 lar classes of plants, this has been separated, and found to 

 contain twice the quantity of sulphur found in other plants, 

 and all these plants contain rather more sulphur, perhaps, 

 than other classes of plants ; and a part of the effect of su- 

 perphosphate of lime, which is almost a specific fertilizer for 

 turnips, although the phosphoric acid has doubtless something 

 to do with it, comes from the fact that superphosphate of lime 

 always contains half or more than half its weight of sulphate 

 of lime. This class of plants contain a great deal of lime. 

 You find in the ashes of all large-leaved plants, like turnips, 

 beets, and tobacco, large quantities of lime. Still, the action 

 of plaster is not necessarily explained by the effect of its in- 

 gredients. One of the most interesting points in the action 

 of fertilizers is their indirect action, and in the case of plaster, 

 this thing has been studied up, not enough, it is true, to af- 

 ford a full explanation of the whole matter, but so as to give 

 us some very useful indications, and show us that we cannot 

 trace the action of fertilizers to the immediate effect of the 

 elements which they contain. Plaster, for instance, may pro- 

 duce a very useful effect upon the soil where it does not sup- 

 ply the plant with sulphuric acid and lime, which are its in- 

 gredients. The simple fact is, that the elements of a fertilizer 

 do not explain, necessarily, the reason of its action. As an 

 illustration of this, take common salt. You may find hund- 

 reds of instances in which common salt has produced remark- 

 able effects upon crops, while, with the exception of plants 

 of marine origin, like asparagus, if you go through the anal- 

 yses that chemists have made, you will find that plants contain 

 very little soda and very little chlorine, which are the elements 

 of salt. Experiments with almost all kinds of plants show 



