320 SCIENCE AND FRUIT GROWING 



conclusion which has already been rendered probable from the 

 results obtained in experiments with barley (p. 296). 



Crop obtained. Delay in sowing. 



o 4 8 12 16 20 days. 



No other plants present . 100 98 90 101 93 94 



Other plants present . 100 91 70 31 51 37 



The toxic action of one plant on another must give rise to 

 many interesting problems relating to plants when grown in 

 masses. One of these is the behaviour of the outside rows as 

 compared with that of the inner ones. As has been already 

 seen, no appreciable difference exists when there is no root-inter- 

 ference (p. 315), but with plots in the field, where there is root- 

 interference, it generally appears that the outside rows contain 

 the stronger plants. This is most noticeable in experimental 

 plots, where care has been taken that the outer plants have not 

 suffered accidental injury. Occasionally the outer plants appear 

 to be the weaker ones, but this may be an instance where appear- 

 ances are misleading, for in no case where measurements have 

 been made, has this proved to be so, and the superiority observed 

 was much greater than would have been anticipated. To inves- 

 tigate the subject, small plots of mustard were planted at Ridg- 

 mont with different distances allowed between the plants in 

 different cases, and there were also similar plots of wheat; at the 

 same time the examination was extended to wheat grown as a 

 field crop on the light ground at Woburn, and to barley grown 

 at Harpenden. Where a field crop was taken, the outside row 

 had to be " made," by removing, early in the season, the rows 

 which were really the outermost ones, owing to these having 

 become damaged during cultivation. 



n Mustard Wheat Wheat Barley 



(Ridgmont). (Ridgmonf). (Woburn}. (Harpenden). 



Outside . 297 201 200 131 204 161 126 

 Inner . 100 100 100 100 TOO 100 100 



The above values, which refer to the relative weights of the 

 whole plants after drying, show that the excess in favour of the 

 outside plants is always very considerable, and may amount to 

 as much as 200 per cent. in several cases it reached 100 per 

 cent. 1 



1 Similar experiments have been made in India on cotton, sorghum, 

 wheat and other crops. J. Fletcher : " Note on a Toxic Substance Excreted 

 by the Roots of Plants." Mem. Dept. of Agric. in India, 1908, ii. 3, pp. 1-17. 



