1 87 
Pickering . — The Effect of one Plant on Another . 
i *8 inch apart), or with from sixteen down almost to one plant of tobacco ; 
whilst in unmanured ground in the field,. the equality holds good within 
a wider range, even to plantations with more than 6 inches between the 
plants in the case of mustard. At the same time, also, the outside rows of 
plants are very much superior to the inner plants. 
This latter superiority is one which is continually noticed in field 
experiments, though the reverse, judging by mere appearances, sometimes 
obtains. Whether, when the outside plants appear the worse, they are so 
in reality, may be doubted ; at any rate, in all the cases which have been 
investigated by weighing, it is a superiority which has existed. But 
appearances would never have led to a correct estimate of the magnitude 
of this superiority, for these outside plants are often ioo to 200 per cent, 
greater in weight than the inside ones. The row next to the outside one 
generally shows some superiority, but the effect of an external position 
extends to only about 6 inches from the edge of the plot. 
The extra vigour of the outside plants is generally attributed to the 
extra manure which they have to draw upon ; but another factor must 
now be reckoned with, in the extra facility offered for the oxidation of the 
toxin at the edge of the plot ; and this appears to be an important factor. 
The question is being investigated on three lines : manure beyond a certain 
limit does not benefit, and even injures a plant ; if, therefore, in a plot 
where the manure has already attained such a limit, we still find that the 
outside plants show a superiority, this cannot be due to any further surplus 
of manure. Such a superiority, we find, still exists in ground manured 
with 100 tons of dung to the acre, and the superiority is little less, if less 
at all, than in unmanured ground. But these experiments require repetition 
and extension before definite conclusions can be drawn from them. 
