88 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY, 



and Irish sources. The stocks marked * were a particularly fine 

 sample of seed which had made no attempt to sprout before it reached 

 us to be put into trays, although the season for sprouting was fairly 

 well advanced, and it is doubtless to the treatment the tubers received 

 while in store that a part of their superiority in yield is due. These 

 results, taken with those to which reference has been made already, 

 seem to show the conditions on the edge of Dartmoor near Moreton- 

 hampstead are suitable for the production of almost or quite as good 

 seed as Scotland and Ireland. To have a good situation for growing 

 seed-potatos so near is manifestly desirable to growers in the south, 

 as it reduces the distance the tubers have to be carried by rail and 

 the consequent risks. 



Exactly what the conditions necessary for the production of 

 good seed are is still obscure. That the locality alone is sufficient 

 to secure seed which will be certain to produce good crops is clearly 

 unlikely, for the crops produced by the seed from Edinburgh, as shown 

 by the foregoing Table, were in 191 8 much below the average from 

 that source. Probably a combination of certain weather and soil 

 conditions are most important, especially perhaps equable con- 

 ditions of moisture and temperature in the soil during the growth 

 and maturation of the tubers. The power of giving increased yield 

 is usually ascribed to immaturity of the crop at lifting time, and 

 certain experimental results appear to confirm that view, but it 

 seems doubtful whether that is the whole story. It is strange, if 

 immaturity alone is responsible for the power of giving increased yields, 

 that so often the power is still retained by the next vegetative genera- 

 tion, and indeed is often increased. For instance, a Scotch stock of 

 ' Great Scot ' gave at Wisley in 1917 from forty tubers 111/2 lb., while 

 forty of the tubers of this stock planted under similar circumstances 

 in 1918, when the general average of potato yields was certainly no 

 higher than in 1917, gave 169I lb. It is at any rate clear that the 

 whole of the factors that' make for maximum yields of potatos are 

 not yet known, although, speaking in general terms, the source of the 

 seed is one of the most important of them. 



