328 HOW CROPS FEED. 



of the crops, and subtracting from that sum the ash of 

 the seeds, together Avith the matters made soUible in the 

 same soils, which had sustained no pLints, but which had 

 been treated otherwise in a similar manner. 



MATTERS DISSOLVED BY ACTION OF ROOTS. 



On 9 lbs. of On 11 lbs. of 

 sandstone. basalt. 



Of 3 lupin plants 0. COS grams. 0.749 grams. 



3 pea " 0.481 " 0.713 " 



20spurry " 0.268 " 0.365 " 



lObuckwh't" 0.332 " 0.327 " 



4 vetch " 0.221 " 0.251 " 



8 wheat " 0.027 " 0.196 " 



8 rye " 0.014 " 0.132 " 



These trials appear to show conclusively that plants 

 exert a decided effect on the soil. We are not informed, 

 however, what particular substances are rendered soluble 

 under this influence. 



We conclude, tiien, that the direct action of the roots 

 of a crop may in all cases contribute toward supplying it 

 with food, and in many instances may be absolutely 

 essential to its satisfactory growth. 



Further Notice of Matters Soluble in Water.— The 



analyses we have quoted sliow that every chemical ele- 

 ment of the soil may pass into aqueous solution. They 

 also show that some substances are dissolved more easily 

 and in greater quantity than others. 



In general, chlorine, nitric acid, and sulphuric acid, 

 are most readily and completely taken up by water, and, 

 for the most part, in combination with lime, soda, and, 

 magnesia. In some cases, sulphuric acid appears to exist 

 in a difficultly soluble condition ( Fan Bemmelen, Ys. 

 St., VIII., 263). 



Potash, ammonia, oaride of iron, (/lamina, silica, and 

 phosphoric acid, are tlie substances which are usually 

 soluble in but small proportion. These, together with 



