1 82 Pickering . — The Effect of one Plant on Another. 
pears, plums, cherries, six kinds of forest trees, mustard, tobacco, tomatoes, 
barley, clover and two varieties of grasses ; whilst the plants exercising this 
baleful influence have been apple seedlings, mustard, tobacco, tomatoes, two 
varieties of clover and sixteen varieties of grasses. In no case have negative 
results been obtained. The extent of the effect varies very greatly: in pot 
Fig. i. Fig. 2. Fig. 3. 
experiments the maximum reduction in growth of the plants affected has been 
97 per cent., the minimum 6 per cent., whilst in field experiments with trees, 
the effect may vary from a small quantity up to that sufficient to cause the 
death of the tree. The average effect in pot experiments may be roughly 
placed at a reduction of one-half to two-thirds of the normal growth of the 
plant, but no sufficient evidence has yet been obtained to justify the con- 
