186 The Roots of the Wheat Plant. 



admit the conclusions concerning the rationale of the action of 

 these as explained by the chemist, namely, that the ammonia 

 given off in the chemical changes of the manure is absorbed 

 by the soil or moisture surrounding the plants and from which 

 they feed by their roots, yet I cannot help thinking that here 

 is a new element in the argument. 



While we look over a wheat-field on a fine sunny day as 

 summer advances, and see the dazzling dancing in the atmos- 

 phere a few feet over the plants, which is caused by the eva- 

 poration of water through the cellular system of the leaves, we 

 may know that the crop is pumping up its food from the soil, 

 but as this is just the time for liberating ammonia also from the 

 soil, there is, I think, reason to believe that the atmosphere 

 charged with carbonic acid and ammonia is at this very time 

 being eagerly respired, and the reason for the development of 

 root keeping pace with that of leaves, is that the functions of 

 these two important organs should be duly balanced. 



Wheat, in its groioing histoi^j is completed in a few weeks, 

 although the production of strong plants for growth occupies, in the 

 winter varieties, many months : and it is just as the neio growth com- 

 mences that ammoniacal manures are so beneficial, as the nitrogen 

 therefrom has to be eliminated in a short time, and as the leaves 

 are small and upright : if we suppose ammonia to be respired by 

 them, they will require a quicker, and more constant and greater 

 discharge of this gas, commencing too at a certain time, than is 

 the case with a plant with large leaves which grow without any 

 serious interruption from their birth, and whose under surface is 

 the only inhaling one, and which is so arranged as to insure the 

 due but more gradual and more certain performance of this office 

 without loss ; and hence, farm-yard manure, which is buried in 

 the soil and which gradually decomposes, at first slowly, but 

 faster the longer it is exposed to atmospheric and chemical 

 actions, giving its inorganic matters in solution through the roots, 

 whilst ammonia is given off into the atmosphere; indeed, so 

 quickly in some of the warm, close days of the early part of 

 September, that every farmer knows when this valuable crop is 

 growing fast by the peculiar odour that he is then aware of in 

 passing a turnip-field. 



These remarks, though offered with a great degree of diffidence, 

 as time for thought and experiment is wanting for its clearer 

 elucidation, yet seems to open up a wide field for inquiry ; at all 

 events they would seem to show that, however complete our 

 chemistry may be, yet in applying it to plant-growth the dif- 

 ferences in the structure and habits of the plants must not be 

 overlooked. 



As regards the use of manures, the foregoing remarks would 



