BEHAVIOUR OF PLANTS IN MASSES 321 



The superiority of the outer rows is generally attributed to 

 the plants in them being able to draw supplies from the ground 

 outside the plot, and thus obtain extra nourishment : but it is 

 extremely improbable that the excess obtainable in this way 

 would ever be sufficient to account for an increased growth 

 of 100 and 200 per cent. It seems certain now that toxic action 

 must play some part, probably the chief part, in the results, the 

 outer plants receiving a smaller dose of toxin than those with 

 neighbouring plants on either side of them. To obtain evidence 

 on this point, plantations of mustard were grown in ground 

 so highly manured that additional manure would produce no 

 further effect, so that, in that case, if the outer rows still showed 

 a superiority, this could not be due to the extra food available. 

 The dose of manure extended up to 300 tons of dung to the 

 acre, and the ground was dressed one yard beyond the limits of 

 the plots containing the plants, of which there were 169 in each 

 plot. The results, of which a summary is given below, showed 

 that the limit at which additional dung ceased to have any 

 further effect on the plants was about 100 tons to the acre, any 

 increase beyond that dose producing, in fact, a slightly dele- 

 terious effect ; l yet with the plants receiving these heavy dressings, 

 the outside rows still showed a superiority over the inner ones, 

 even to the extent of nearly 100 per cent., proving conclusively 

 that this superiority cannot be attributed to the extra nourish- 

 ment received. 



Tons dung to the acre o 12 J 25 50 100 200 300 

 Average weight of 1 



inner plants (grs.) / 35 6l 

 Relative weight of \ 



outside plants . . I 251 232 249 181 240 173 165 



(Inner plants = 100) J " ~^8~~ ~~I93~ 



Where the dunging is not excessive, some portion of the 

 superiority of the outer rows may be attributed to the extra 

 nourishment received by them, for in that case the superiority 

 is greater (228) than where the dunging has been excessive (193) ; 

 indicating that in ordinary circumstances about one-quarter of 

 the superiority ( is due to the extra food, and three-quarters to 

 the decrease in toxic effect. But these proportions would, of 

 course, vary with different plants. 



1 These values are based on the green weights of the plants : the dry 

 weights, which were subsequently determined, led to the same conclusions, 

 except that they gave the maximum effect of the dung as occurring at 200, 

 instead of 100, tons to the acre. 

 Y 



