298 SCIENCE AND FRUIT GROWING 



, the mean values in the otjier nine series gave for relative vigour 

 of the plants affected by the surface growth 



22'6 when measured earlier. 

 30 '7 when measured later. 



That the effect of the surface crop on the plant in the pot 

 must be due to something which is washed down from the 

 former on to the latter, is as evident as in the similar 

 experiments with trees and grass (p. 285), but in this case a 

 modification in the experiment was made which still further 

 excluded the possibility of any other explanation. This modifi- 

 cation consisted in growing a surface crop equally in two sets 

 of pots, but, whereas in the one, teachings from the crop in 

 the trays were allowed to soak through to the plant in the 

 pots, in the other, this was prevented by blocking the holes in 

 the trays. The effect on the plants in the pots in this latter 

 case was found to be practically nil. The pots numbered 1795 

 and 1794 in Fig. 42 illustrate the results with and without a 

 surface crop when the holes in the trays were blocked, the 

 average difference between the plants in those cases being 

 ii per cent. a value less than the experimental error, which, 

 as will be seen from the details entered below, is large, owing to 

 difficulties arising in adjusting the water supplied to the plant 

 whereas when the trays were perforated, the surface crop reduced 

 the growth of the plants in the pot by as much as 63 per cent. 



Relative Weights of plants with and without a surface crop. 

 Trays not perforated. 



Without surface crop . . . T OQ r 100 



ooj 



With surface crop .... 7 5|^9 



Trays perforat 



Without surface crop . . . . I ^ I 100 



VD ) 



With surface crop . . . . 4 1 37 



This experiment affords evidence on another point of great 

 general importance. It may be seen from the figure that the 

 crop of mustard in the unperforated tray (1795) is much lighter 

 than that in the perforated one (1792), and this was so in every 

 case, in spite of the utmost care being taken to foster its growth : 

 the relative weights of the surface crops in the two classes of 

 trays were as 100 to 45. The explanation of this is evident: 



