72 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



above crops on the outside border, except for the rye, which occupied 

 the belt of ground utilized for isolating the experimental beds of 

 Series I. and Series II. 



The plants were examined from the seedling stage onward 

 throughout the growing season, and, except in the case of onions, 

 the various crops were unaffected with eelworm. The results of the 

 experiments clearly show that onions should not follow in immediate 

 succession on land which has borne a diseased crop of Narcissi. The 

 behaviour of the other crops coincides with the results of experiments 

 made by Ritzema Bos in 1910, by which he formulated his biological 

 strain theory, which, in brief, is that Tylenchus devastatrix becomes 

 so adapted to a particular species of host plant that it will not attack 

 with any severity any other species. 



In conjunction with the above experiments, pot culture experi- 

 ments were made at Wisley. Six-inch pots of sterilized soil were 

 sown with rye, winter and spring oats, broad beans, wheat, buck- 

 wheat, clover, lucerne, peas, and onions. The pots were watered once 

 with water containing eelworms grown in pure culture. There again 

 onions were the only plants affected with the eelworm, and the photo- 

 graph clearly illustrates the deformed growth of the affected seedling 

 plants (fig. 19). 



XXXIII. — The Effect of " Place " on Yield of Crops. 



By F. J. Chittenden, F.L.S., V.M.H. 



In a note on the effect of position on the yield of plants * it was shown 

 that the outer row of a plot of turnips, having a greater space and 

 therefore both a greater volume of soil from which to draw supplies 

 and better illumination, gave a greater yield than either of the inner 

 ones otherwise similarly treated. 



In some experimental plots of potatos the opportunity occurred 

 to test the effect of " place " upon the yield of this crop, and. as will be 

 seen, it proves remarkably sensitive. 



The arrangement of the plots is shown in the plan (fig. 20). There 

 were sixteen plots in pairs, each planted so that several feet separated 

 the first row of potatos from other plants, four or five feet also separated 

 the outermost of the plants on one pair of plots from those on 

 the next pair. Each plot had three rows of potato ' Up-to- 

 Date ' planted on its eastern side (rows A, B, C), and these were 

 followed towards the west by rows of other varieties, all the rows 

 equal distances apart, and each row contained eighteen plants equally 

 distributed along it. The different plots each received different treat- 

 ment, but the treatment of all the plants on any one plot was the 

 same. 



We are only now concerned with the plants of ' Up-to-Date,' of 

 which each plot carried fifty-four. Eighteen of these formed the 



* In Jour* d R.H.S. xli. p. 68. 



