14C-tracer experiments showed that the export of assimilates labelled with a short pulse of 14CO2 continued for 5 weeks. There appeared to be an approximately exponential loss of ethanol-insoluble 14C from the haulm with a half-time of about 3.5 weeks. Initially there was a poor correlation between the fresh weight of the tubers and their 14C content but the correlation became good after 5 weeks. Field data showed that, in many instances, the rate of tuber growth was greater than the rate of growth of the whole plant. This suggests the transfer of large amounts of dry matter from the haulm to the tubers. Dry-matter loss from the haulm could account for the discrepancy and the amount transferred in this way was about 10 per cent of the final dry weight of the tuber. There was an increase in net assimilation rate when the leaf area of the plants started to decline. It is suggested that this increase was due to an increase in the rate of photosynthesis brought about by the influence of the rapidly growing tubers.
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J. M. Moorby (1970) studied this question.