198 HOW CROPS GROW. 
est in those parts of the plant which, on this view, would 
most require its presence. Thus N orton, (Am. Jour. of 
Sci., [2,] vol. iii, pp. 285-6,) found that in the sandy oat 
the upper half of the dry leaf yielded 16.2 per cent ash, 
while the lower half gave but 13.6 per cent. The ash of 
the upper part contained 52.1 per cent of silica, while that 
from the bottom part had but 47.8 per cent of this ingre- 
dient. According to Arendt, (Das Wachsthum der-Ha- 
Serpflanze, p. 180,) the different parts of the oat contain 
the following quantities of silica respectively : 
Amount of silica in 1000 parts of dry substance. 
Removed Insoluble 
by water. in water. Total. 
Lower part of the stem..... 0.33 14 17 
Middle part of the stem....0.30 4.8 5.1 
Upper part of the stem..... 0.36 13.0 13.3 
Lower leaves............005 0.86 34.3 35.2 
Upper leaves..........0.005 0.52 43.3 43.8 
“We see then, plainly, that the upper part of the stem 
and leaves contains more silica than the lower parts, while 
the lower parts certainly” need to possess the greatest 
degree of strength. 
We must not forget, however, as Knop has remarked, 
that the lower part of the leaf of most cereals and grasses 
which envelopes the stem like a sheath, is really the support 
of the plant as much as, or even more, than the stem itself. 
The results of the many experiments in water-culture 
by Sachs, Knop, Wolff, and others, (see p. 186,) in which 
the supply of silica has been reduced to an extremely 
small amount, without detriment to the development of 
plants, commonly rich in this substance, would seem to 
demonstrate that silica does not essentially contribute to 
the stiffness of the stem. 
Wolff distinctly informs us that the maize and oat plants 
produced by him, in solutions nearly free from silica, 
were as firm in stalk, and as little inclined to lodge or 
“Jay,” as those which grew in the field. 
