THE ASH OF PLANTS. 187 



Knop inclined to believe that the little silica he found 

 in his maize plant was due to dust, and did not belong to 

 the tissues of the plant. He remarked, " I believe that 

 silica is not to be classed among the nutritive elements of 

 the Graminese, since I have made similar observations in 

 the analysis of the ashes of barley." 



In the numerous experiments that have been made more 

 recently upon the growth of plants in aqueous solutions, 

 by Sachs, Knop, Nobbe & Siegert, Stohmann, Rauten- 

 berg & Kiihn, Birner & Lucanus, Leydhecker, Wolff, 

 and Hampe, silica, in nearly all cases, has been excluded, so 

 far as it is possible to do so in the use of glass vessels. 

 This has been done without prejudice to the development 

 of the plants. JSTobbe & Siegert and Wolff especially 

 have succeeded in producing buckwheat, maize, and the 

 oat, in full perfection of size and parts, with this exclusion 

 of silica. 



Wolff, ( Vs. /St., VIII, p. 200,) obtained in the ash of 

 maize thus cultivated, 2-3 | of silica, while the same two 

 varieties from the field contained in their ash 11-| 13| . 

 The proportion of ash was essentially the same in both 

 cases, viz., about 6| . Wolff's results with the oat plant 

 were entirely similar. Birner & Lucanus, ( Vs. /St., VIII, 

 141,) found that the supply of soluble silicates to the oat 

 made its ash very rich in silica, (40 | ,) but diminished the 

 growth of straw, without affecting that of the seed, as 

 compared with plants nearly destitute of silica. 



While it is not thus demonstrated that utter absence of 

 silica is no hindrance to the growth of plants which are 

 ordinarily rich in this substance, it is certain that very 

 little will suffice their needs, and highly probable that it 

 is in no way essential to their physiological development. 



The Ash-Ingredients, which are indispensable to Crops, 

 may he taken up in larger quantity than is essential. 



More than sixty years ago, Saussure described a simple 



