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 Graminez, 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 & Kiithn, 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. Nobbe & 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. S¢., VII, 
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 be taken up in larger quantity than is essential.— 
More than sixty years ago, Saussure described a simple 
