126 FERTILIZERS UN SANDY SOIL — SMITH. 



to scxliuin and silicon the case is different, and we will take- 

 time to point out that probably these are not required for plants, 

 — especially as it is often erroneously taught that plants require 

 them, particularly the latter, to strengthen their stalks. It 

 appears from experiments that sodium cannot be wholly excluded 

 from plants on account of its universality, but that in so far as 

 it is or can be excluded, the plants do not suffer for it. Silicon 

 is always present in the plant wdien grown under natural con- 

 ditions. It occurs in largest proportions in the outer portions of 

 the plant, especially the bark and leaves, and in the parts sur- 

 rounding the seeds. It varies very much in the same and in 

 different plants. The amount present depends on the amount of 

 it soluble in the soil. Sachs has shown that the amount in the ash 

 of the Indian corn could readily be reduced from 18^ to 7|^ with- 

 out injuring the growth in the least. Knop grew. a maize plant 

 with 140 ripe kernels in a medium so free from silicon that there 

 was only a trace of it found in the root, b.ut half a milligram in 

 the stem, only 22 milligrams in the leaves, and none in the 

 seed. Knop thought that the little that he found was due to dust 

 and was not present in the tissues. He says, " I believe that 

 silica is not to be classed among the nutritive elements of the 

 Graminet^, since I have made similar observations in the analysis^ 

 of barley." In experiments conducted by Sachs, Knop, Nobbe, 

 and Siegert, Stohmann, Ra,ute, Rautenberg and Kuhn, Birner and 

 Lucanus, Leydbecker, Wolff and Hampe, it was, as far as possible^ 

 excluded from the food of plants grown in glass vessels, without 

 any injurious effects to the plants. A number of plants of different 

 species have been grown to full development without an appreci- 

 able amount of it being present. 



Davy supposed that the function of silicon was to serve as a 

 support to the plant as bones do to the body of an animal. But 

 we find that the proportion of silicon is not greatest in those 

 parts which require the greatest strength. The analysis of the 

 oat shows that the upper part of the stem and leaves contain 

 more silicon than the lower part of the stem, which certainly 

 requires to be the strongest. In the experiments above, the 

 stem was not weakened in the least when grown without this 



