PLANT GROWTH. 433 



quite obvious tliat the time-honored practice of using wood 

 ashes, or lime, or marl, etc., above referred to, for manurial 

 purposes, presents quite a different aspect to us from any 

 that it could possibly claim in previous ages ; for knowing 

 now, in consequence of previous careful analysis of the 

 ashes of its particular kind, what elements the perfect plant 

 contains, the practical experience of the past receives a 

 more intelligent interpretation of its results, and future 

 success a better chance. 



The direction which Liebig's genius has given to the 

 stud}^ of plant growth, with reference to its application in 

 practical agriculture, has been pursued since with an interest 

 and success unparalleled in the history of any province of 

 science. Practice and science have already for years 

 worked hand in hand to study the influence of physical 

 and chemical agencies on the production of vegetable 

 growth, and to reconcile real and apparent differences of 

 experimental results. 



Much has been accomplished — too much, in fact, to find 

 here a mere passing enumeration ; yet much more remains 

 to be learned to free our present system of manuring from 

 that degree of uncertainty which a reasonable prospect of 

 success still demands. The unsatisfactory condition of our 

 current modes of fertilizing our lands is, in a great measure, 

 due either to limited information or almost entire io'norance 

 concerning the following points : — 



1. AVhat are the mutual physical and chemical reactions 

 of the various kinds of soil on the different materials we 

 apply for fertilizing purposes? In other words, what 

 becomes of the fertilizer in the soil ? 



2. In what jjarticular form do the different plants absorb 

 the various kinds of mineral plant food ? 



3. What are the specific functions of the different mineral 

 substances of the plant food in the life of plants? What 

 effect do they produce when applied in different combina- 

 tion ? 



The history of all well-conducted field experiments points 

 upon every page to the necessity of a closer study of every 

 one of the above specified points, before any material 

 improvement in our present mode of fertilizing our lands 



