216 GUANO. 



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 neces- 

 sity of potash for vegetation, and that a supply is re- 

 quired by fields poor in that ingredient, or drained of 

 it ; but the question as to the importance of magnesia 

 for seed formation has not, as yet, met with the same 

 attention, and special experiments in this direction 

 would be very desirable. The fact that much more 

 magnesia is found in the seeds than in the straw unmis- 

 takably shows that it must play a definite part in the 

 formation of the seed, which might, perhaps, be ascer- 

 tained by a careful examination of seeds of the same 

 variety of plants containing different amounts of mag- 

 nesia. It is a well-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 lat- 

 ter may, in the formation of the seeds, be essentially in- 

 fluenced by the presence of lime or of magnesia, so that 

 the differences in the proportions of both of these alka- 

 line earths may have a certain connection with the pres- 

 ence of the soluble nitrogenous compounds (albumen 

 and casein), or of the insoluble (gluten or vegetable 

 fibrine). Of course, the quantity of potash and soda 

 present would have to be taken into account in an in- 

 vestigation of the kind. The fertilising action of guano 

 is generally attributed to the ammonia in it, and to the 

 other ingredients rich in nitrogen ; but accurate experi- 



