198 now CROPS GROW. 



est in those parts of the plant which, on this view, would 

 most require its presence. Thus Norton, (Am. Jour, of 

 JSci.j [2,] vol. iii, pp. 235-6,) 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- 

 ferpflanze, p. 180,) the different parts of the oat contain 

 the following quantities of silica respectively : 



Amount of silica in 1000 part* of dry substance. 



Removed Insoluble 



by water. in water. Total. 



Lower part of the stem 0.33 1.4 1.7 



Middle part of the stem 0.30 4.8 5.1 



Upper part of the stem 0.36 13.0 13.3 



Lower leaves 0.86 34.3 35.2 



Upper leaves v 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 

 " lay," as those which grew in the field. 



