THE BIOLOGY OF SOIL. 65 



tributions which have been furnished, and are still 

 being furnished by the chemist; and I for one 

 hope that his labours will continue to go hand in 

 hand with those of the physiologist. 



But, when all due honour is paid to the 

 scientific chemist, it must still be allowed that his 

 problems are different from the real problems of 

 agriculture. To take one set of instances alone. 

 The chemist can analyse a given soil or a given 

 manure, and can even go a long way towards 

 making them, but his analyses do not tell us 

 what conditions are necessary in order that their 

 ingredients may be presented to the roots so as 

 to be absorbed and become built up into the 

 plant. Chemistry told us that carbon was fixed 

 from the air, but physiological experiments de- 

 termined how this meant the synthesis of certain 

 definite carbohydrates this, too, in the face of 

 the powerful authority of the chemist Liebig, who 

 supposed that the vegetable acids were the results 

 of the assimilation of carbon. Wolff, De Saussure, 

 and other chemists have done yeoman service in 

 showing that different plants, growing in the 

 same soil, contain different proportions of mineral 

 substances; but it was by means of water-cultures, 

 and other physiological researches, such as those of 

 Pfeffer on osmotic phenomena and of Schwarz and 

 Molisch on root-hairs, that the puzzling question of 

 selective absorption, by means of the living root- 

 hairs, came into the arena of our knowledge. 



In every case and, as already said, I am not 

 undervaluing the work done^ the chemist has left 



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