1 86 Pickering. — The Effect of one Plant on Another. 
growth, some two or three months later, the last sown plants are 60 to 
70 per cent, smaller than the others. It is evident that three four-day-old 
seedlings could not have exhausted the nourishment in kilos of rich 
soil so far as to leave insufficient food for three other seedlings ; nor can 
a difference in age of four days in a total life of several months account 
for such a difference in the weights of the plants. But the results become 
clear if we take into account the toxic effect of one plant on the other, for 
the later planted individuals have to start growth under toxic conditions 
which were absent in the case of those first planted, and throughout their 
existence their inferiority in size will make them suffer more than their 
stronger brethren, though the actual amount of toxin in the soil is the 
same for all. Yet it is found that they are not altogether without their 
revenge, for the toxin formed by them affects to a certain extent the older 
plants, and this effect may be traced, even when the feebler plants are only 
about one-tenth the size of stronger ones. The importance in practice of 
having seed which will germinate uniformly at the same time, or in having 
plants of uniform growth in a bed, is demonstrated by these experiments ; 
for a difference of only four days in the germination of one-half of the seeds 
in the case of mustard reduces the total weight of the whole crop eventually 
obtained by as much as 20 per cent. 
The divided pots have been utilized to ascertain what the effect of 
crowding in a plantation is when there is no root-interference. In 
appearance the results were remarkable, for with mustard and tobacco 
plants at distances of 4, 6 and 9 inches apart, the plants were considerably 
smaller as the distances between them were greater, the deficiency in their 
height extending up to 30 and even 50 per cent., and they appeared 
to be in every way inferior. But these appearances were entirely mis- 
leading, for it was found that the weights of the plants were the same 
at whatever distance they were planted, and at whatever age they were 
lifted ; moreover, this equality held good throughout the plantation, even 
including the outermost rows : thus interference of the above-ground portions 
of plants does not affect the amount of growth, but only the quality of that 
growth. 
The results are very different, however, when there is root-interference, 
as when a number of plants are grown together in one pot, or in one plot 
in the field ; and when the crowding attains to a certain magnitude, the 
limiting factor is the amount of soil available for each plant : the result of 
which is that the weights of the plants are inversely proportional to the 
bulk of soil available (which with soil of uniform depth is synonymous 
with the area), or, in other words, the total plant-growth is the same, 
whatever be the number of plants. Thus, in pots containing 7j kilos of 
rich soil the total crop was the same with from sixty-four down to sixteen 
mustard plants (the latter number representing plants at a distance of 
