296 SCIENCE AND FRUIT GROWING 



of the plant either in the pots or the trays, similar variations 

 were obtained in different seasons : thus 



Plant in Plant in Relative vigour of the 



the pots, the trays. plants in the pots. 



6 series Mustard Mustard (i to 40 =) 21 



4 ,, Tobacco Grass (29 to 78 =) 60 



2 ,, Mustard Grass (42 to 54 =) 48 



To these, in order to make the list of experiments complete, 

 may be added 



Relative vigour of the 



plants in the pots. 



i series Barley Grass 85 



16 

 24 



3i 

 36 

 33 



The variations in comparable series were sometimes traceable 

 to exceptionally great or small vigour of the growth in the trays, 

 but the more frequent cause was evidently due to variations in 

 the rapidity of growth of the seedlings in the pots, as conditioned 

 by atmospheric peculiarities ; for, where growth was slow, as when 

 the season was unsuitable, the plants in the pots were subjected, 

 while they were still young and in a susceptible condition, to 

 the baleful influence of the surface crop for an exceptionally 

 long time, and the stunting was much greater than where growth 

 had been rapid. 



So far as any comparison can be made, the action of a surface 

 crop on these soft-wooded plants is quite as great as that of 

 grass on trees, probably greater; it reduces the vigour of the 

 plant to an amount which may be roughly averaged at 40 per 

 cent, of what its vigour is in the absence of a surface crop, whilst 

 in the case of the action of grass on trees, the average reduction 

 may be placed at about 50 per cent, after two or three years' 

 growth. But the cases are very different, for with hard-wooded 

 plants the effect is cumulative, owing to the action extending 

 over successive seasons, and, as has been seen, this cumulation 

 of effect may eventually result in the death of the tree. Cer- 

 tainly these results do not indicate that grass has any excep- 

 tionally baleful influence as compared with other crops, rather 



