BEHAVIOUR OF PLANTS IN MASSES 319 



already growing. A glance at the numbers quoted above shows 

 how great that injury may be, for even when the second-sown 

 plants are only half the size of the first (third to fourth entries), 

 they reduce the vigour of the first plants to 60 per cent, of what 

 it would have been if they had been left to develop alone (from 

 198 to 124). 



A familiar instance where the co-existence of plants of different 

 degrees of vigour gives unsatisfactory results is where gaps in 

 an established orchard are filled up by planting young trees : 

 but in that case there may often be other causes such as 

 shading, etc. which contribute to the unsatisfactoriness of the 

 results ; the exhaustion of the ground by the previous occupier 

 cannot, however, be reckoned amongst these causes, as was 

 shown by the Woburn results of growing crops on former tree- 

 sites (p. 301). 



In the experiments last described, part of the reduction in 

 weight of the second-sown plants must be attributed to the 

 shorter time allowed to them for their growth; but reduction 

 from this cause did not amount to much, as was proved by 

 growing six plants in separate pots for the same lengths of 

 time as in the experiment itself. The relative weights of the 

 plants when the sowings were delayed by periods ranging up to 

 20 days are given in the first line below, whereas the weights 

 of the second-sown plants in the experiments already quoted 

 are those reproduced in the second line. 



Crop obtained. Delay in Sowing. 



o 4 8 12 16 20 days. 



No other plants present . 100 100 87 81 81 60 

 Other plants present . 100 78 75 45 40 19 



All these experiments were repeated with wheat. The diffi- 

 culty of growing this crop in such small pots, and the fact that 

 some of the plants became affected with smut, prevented the 

 results from being sufficiently accurate for treatment in the way 

 that the mustard results have been treated on p. 317 ; but it is 

 clear from the following values that the general behaviour of the 

 wheat was similar to that of the mustard, the inferiority of the 

 second-sown plants (second line) being in no way explicable on 

 the grounds of the mere delay in sowing (first line). It is clear, 

 too, that both the effect of delay in sowing, and of the effect of 

 one plant on another when these are of different ages, is con- 

 siderably less in the case of wheat than in that of mustard, a 



