8 



JOI RXAL (^1^ ITTF. ROYAL Ilon'ricriVri UAL BCK'lhyrY. 



Furllionnore. if llic ;tii,il\ s(>s of nil |il;iii(s -avo \cry iimcli nlikc, ;ni 

 even i;i'e;iter siuiibn It \ is show ii lt\ ,'W»ils. TiiMc III. t's llic clKMiiii-;!! 

 aii;il\s(.'s of ,1 iiiiiiil>or o\ soils, ir|>rt.'siMi(,iii<;- piMcticnl ly nil Hit" lype-s 

 met witli 111 tills country, excepl the (I'lu^ j)(\iis. The j^i'entcM- ])[\rl of :i 

 soil C(^nsists iiisohihle iiinterinl whieh is of no ser\ice lo the jilanl-, 

 but in the lest we nlways lind sinnll nnuv.ints of nitrogen. |)hosj)hori(' 

 acid, lime, mn^nesin, etc. ; just the siihsl nnec^s, in fnef, that, we (ind in 



Fig. 7. — Percentage of Rumex Acetosa. 

 For manuring, see fig. 5. 



all plants, and this amomit, if small, is still sufficient for fifty or a 

 hundred years' growth of the plants wliich occupy the land. 



We must not expect, then, to find in the plant that grows thus con- 

 fined to a veiy small area some particular chemical substance which 

 occurs in the soil of that area and nowhere else ; in fact, we can rarely or 

 never trace any such simple and direct action of a particular substance in 

 the soil upon the plant. All plants contain the same elementary sub- 

 stances — carbon, nitrogen, potash, etc.; the differences come in the 

 way these units are corjibined, just as Paris and London are alike built 



