ASH OF GUANO AND SEEDS COMPAKED. 257 



Potash 1-56 to 2-03 



Lime 34'00 „ 37-00 



Magnesia 2-5G „ 2-00 



Phosphoric acid .... 41-00 „ 40-00 



If we compare with this the composition of the ashes 

 of various seeds, we see at once that the incombustible 

 constituents of guano do not altogether replace the soil 

 constituents carried off in the seeds. 



In 100 parts of seed ash are contained, — 



Wheat Peas and beans Rape 



Potash 30 40 24 



Lime 4 6 10 



Magnesia . . . .12 6 10 



Phosphoric acid ... 45 36 36 



The principal difference between the ash of guano 

 and that of these seeds lies in the deficiency of potash 

 and magnesia in the former. 



Agriculturists are generally agreed about the necessity 

 of potash for vegetation, and that a supply is required by 

 fields poor in that ingredient, or drained of it ; but the 

 question as to the importance of magnesia for seed for- 

 mation has not, as yet, met with the same attention, and 

 special experiments in this direction would be very desir- 

 able. The fact that nuich more magnesia is found in the 

 seeds than in the straw unmistakably shows that it must 

 play a definite part in the formation of the seed, which 

 might, perhaps, be ascertained by a careful examination 

 of seeds of the same variety of plants containing different 

 amounts of magnesia. It is a weU-known fact that the 

 seeds of the several species of cereals having the same 

 proportion of nitrogen, do not always contain the same 

 nitrogenous compounds, and it is possible that the nature 

 of the latter may, in the formation of the seeds, be essen- 

 tially influenced by the presence of lime or of magnesia, 

 so tliat tlie differences in the proportions of both of tliese 



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