CHAP, ii.] of Plants. DC Saussure. 501 



elements in the modern theory of the respiration of plants, 

 though he did not fully explain their mutual connection. 



It evidently was the received opinion before the time of 

 Ingen-Houss, and in spite of Hales' views, that plants derive 

 the larger part of their food from the constituents of earth and 

 water. lUit when it became known that the carbon, which is 

 the chief constituent of vegetable substance, comes from the 

 atmosphere, and it was considered that much the larger part of 

 that substance is combustible, it naturally became a question 

 whether the incombustible ingredients which form the ash take 

 any part in the nutrition of plants. This question was by many 

 physiologists answered in the negative ; but de Saussure main- 

 tained the contrary view. He insisted that certain ingredients, 

 which are found in the ash of all plants, must not be regarded 

 as accidental admixtures, and that the small quantities in which 

 they occur are no proof that they are not indispensable ; and 

 he showed from a large number of analyses of vegetable ash, 

 which for a long time were unsurpassed in excellence, that 

 there are certain relations between the presence of certain sub- 

 stances in the ash and the condition of development of the 

 organs of the plant ; for instance, he found that young parts of 

 plants capable of development were rich in alkalies and phos- 

 phoric acid, while older and inactive portions were richest in 

 lime and silicic acid. Still more important were the experi- 

 ments in vegetation, by which he showed that plants, whose 

 roots grow not in earth but in distilled water, only take up as 

 much ash-constituents as corresponds with the particles of dust 

 which fall into the water ; and further, that the increase in the 

 organic combustible substance of a plant so grown is very 

 insignificant, and consequently that there is no normal vege 

 tation where the plant does not take up ash-constituents in 

 sufficient quantity, a result of the highest importance to the 

 main question. Unfortunately de Saussure neglected to state 

 these results with due emphasis and to point out their fun- 

 (liinental importance, and consequently doubts were enter- 



