136 SUGGESTIONS FOR EXPERIMENTS 



it must, therefore, be a more purely chemical function than those 

 substances perform, which, like lime, contribute to the masonry 

 of the system. 



And what thus appears to be true of animals may also be 

 true of plants. Substances may enter into them to perform 

 purely chemical functions, without contributing largely to, or 

 being found to form any considerable part of the fixed substance 

 of the plant. 



If this be so, we cannot judge from the composition of the 

 ash as to the value or desirableness of a given substance, simple 

 or compound, to a given plant. We must not, therefore, attach 

 too much weight to inferences such as I have drawn above (b) 

 as to the probable special adaptation of this sulphate of mag- 

 nesia to crops of corn. We are rather to inquire, by repeated 

 and careful experiment, whether such inferences are supported 

 or confuted by experiment. In fact, among the higher uses of 

 field experiment are those of testing, not only purely speculative 

 opinions, but the soundness and justness, also, of those deduc- 

 tions to which chemical analyses of various kinds appear natu- 

 rally and fairly to lead. 



6. Suggestions for experiments icith sulphate of magnesia. 



1. The practical man will find nothing very decisive in the two 

 preceding sections, as to the money value of sulphate of magnesia, 

 when applied alone to his usually cultivated crops. As a 

 top-dressing to corn crops it has done good, and the presence of 

 so much magnesia in grain may afford encouragement even to 

 the practical farmer to apply it in spring to wheat, oats, and 

 rye, with the hope of profit. 



Upon potatoes, also, it appears to have done good, both as a 

 top-dressing and as a mixture with the manure, and further 

 trials may safely be made with it. 



2. To the scientific agriculturist, I would recommend 



a The trial of this, compared with the other sulphates, as 

 described when treating of experiments with gypsum in a pre- 

 ceding section. 



b The comparative action of the sulphate of magnesia, upon 

 different crops corn, pulse, hay, and roots. Is the extent of 



