86 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



practice two or three other things beside actual yield need to be taken 

 into consideration, the three most important being the relative quantity 

 of seed required, the convenience in cultivating among and earthing 

 up the plants, and the need of a circulation of air as a preventive of 

 disease. 



It will be seen that the difference in yield between one plot and 

 another so far as ware and seed potatos go is often scarcely more than 

 the weight of the seed planted. Especially with the nine-inch spacing 

 between the plants there is generally a much higher proportion of chats 

 to ware and seed (compare for instance the crops on the 30 in. x 

 9 in. spacing with the 30 in. X 12 in., and that again with the 

 30 in. X 18 in., which proves to be about as economical as the 30 in. 

 X 12 in.). Ir all probability, with a large-topped variety such as 

 ' Arran Chief,' the most remunerative spacing, all things considered, 

 will be somewhere between 2 feet and 2 feet 6 inches between the rows 

 and 15 inches between the plants. 



The spacing of a square yard for. each plant is clearly too great to 

 give a profitable return, but it is by no means clear that it is beyond 

 the point at which the plant's roots cease to occupy the surrounding 

 ground and to profit by the increased space. The curve given in Fig. 24 

 shows the gradual and almost regular rise in yield from average plants 

 in the different spacings, the horizontal distance apart of the crosses 

 which represent these average yields representing the relative space 

 given, and the height of the cross above the base line the respective 

 yield. 



II. — Effect of Different Origin on Yield of Potatos. 



It has long been known that seed-potatos from parts of Scotland and 

 from Ireland tend to give much greater yields, other things being 

 equal, than do those from the middle or most parts of the south of 

 England. This has been repeatedly pointed out in this Journal 

 (see, e.g., vol. xxxiv., p. 538), and is now widely acted upon by 

 large numbers of growers. Figures derived from our trials indicate, 

 however, that not all parts of Scotland are equally good as a 

 source of seed, and confirm a belief quite widely held. The com- 

 parative table already referred to shows, for example, that twenty 

 tubers of ' Up-to-Date ' from Alloa gave 123 lb., while twenty from 

 Ayrshire gave only 68 lb., and from Kelso 56 lb. Somewhat similar 

 discrepancies are to be found in other seasons and between other 

 localities, and the difference is too large to be of no significance, although 

 only twenty plants are brought into comparison. Other figures in 

 various trials suggest that some parts of England are better than others 

 as sources of seed-potatos, and the district near Moretonhampstead 

 on the edge of Dartmoor appeared to be particularly indicated as a 

 good source in more than one of our recent trials. Arrangements 

 were accordingly made in 1918 to obtain seed tubers of certain varieties 

 from different localities, including the Moretonhampstead district, 



