460 



SCIENCE. 



[N. S. Vol. XXII. No. 563. 



the earlier, experimenters with manures 

 used soluble silicates with the idea of there- 

 by increasing the stiffness of straw. But 

 further investigations showed that cereals 

 could be brought to maturity without any 

 supply of silica, and that the stiffness of 

 the straw was a physiological matter in no 

 way conditioned by silica. As a conse- 

 quence this plant constituent has now been 

 disregarded for a long time. But it is idle 

 to suppose that a substance present, for 

 example, to the extent of 60 per cent, or so 

 in the ash of the straw of wheat, has no 

 part to play in the nutrition of the plant. 

 Among the Eothamsted experiments there 

 are fortunately some barley plots which 

 have received soluble silica for many years, 

 and a recent examination of the material 

 grown on these plots begins to cast some 

 light on the function of silica. Its effect 

 upon the plant is in some way parallel to 

 that of phosphoric acid ; on the plots which 

 have had no phosphatic manure for more 

 than fifty years an addition of soluble silica 

 increases the crop, increases the proportion 

 of grain and hastens the maturity in ex- 

 actly the same fashion, though to a less 

 degree, than an addition of phosphoric 

 acid. The results point to the plant rather 

 than the soil as being the seat of the action ; 

 a plant that is being starved of phosphoric 

 acid can economize and make more use of 

 its restricted portion if a quantity of sol- 

 uble silica be available. There is no possi- 

 bility of replacing phosphoric acid by silica 

 in the general nutrition of the plant, but 

 the abundance of silica at the disposal of 

 the cereals certainly enables them to di- 

 minish their call for phosphoric acid from 

 the soil. 



Much in the same direction lie the re- 

 searches which are being pursued with so 

 much vigor by Loew and his pupils in 

 Japan on the stimulus to assimilation and 

 plant development which is brought about 

 by infinitesimal traces of many metallic 



salts not usually recognized as being pres- 

 ent in plants at all. It has been often 

 recognized that substances which are toxic 

 to the cell in ordinary dilutions may, when 

 the dilution is pushed to an extreme, reach 

 a point at which their action is reversed 

 and begins to stimulate. Probably some of 

 the materials used as fungicides and in- 

 hibitors of disease act in this fashion by 

 strengthening the whole constitution of the 

 plant rather than by directly destroying or 

 checking the growth of the fungus my- 

 celium. The subject is certainly one which 

 promises to yield results of value in prac- 

 tise, and calls for more extended and exact 

 observation. 



The importance of research on the par- 

 ticular function of the various constituents 

 of the crop lies in the fact that it is only 

 by the possession of such knowledge we 

 may possibly infiuence in desired directions 

 the quality of our crops. With the effect 

 of manuring upon the yield of most of our 

 crops we are now familiar, but the question 

 of ' quality, ' almost as important as that of 

 yield, forms a more difficult problem. One 

 particular example may be cited, that of 

 wheat, because of late years it has been a 

 subject of investigation in. most wheat-pro- 

 ducing countries. That quality of wheat 

 which is of special commercial importance 

 is its so-called 'strength,' the capacity of 

 yielding flour of such a consistency in the 

 state of dough as will retain the gases pro- 

 duced in fermentation with the formation 

 of a tall, well-piled loaf. This property of 

 'strength' is usually found in a hard horny 

 and translucent grain, the soft, mealy -look- 

 ing wheats being as a rule ' weak. ' Again, 

 the strong wheats usually originate from 

 districts like the Hungarian plain, the 

 Northwest of America, and south Russia, 

 countries characterized by a typical conti- 

 nental climate, cold and dry in the winter, 

 with rains in the late spring and early 

 summer, and a gradually increasing dry- 



