368 Carbo/ii/dnifcs of the Lrnf of the Potato 



rises the saccharose increases along practically a straight line, which 

 runs more or less closely parallel to the temperature curve. The 

 maximum of saccharose is, however, reached earher than the tempera- 

 ture maximum, viz. at 2 p.m.; after this the saccharose falls continu- 

 ously along nearly a straight line, throughout the rest of the day and 

 night, until sunrise next morning. The range of variation during the 

 24 hours is from 1-70 to 3-66 per cent. 



The hcxoses are present in relatively small amount and during the 

 day fluctuate far more, and less regularly, than the cane sugar: the 

 total variation is only from 0-4 to 1-2 per cent. The small changes in 

 the hexoses between 6 a.m. and 2 p.m. synchronise with small changes 

 in the starch present in the leaf, as if interconversion of these substances 

 occurred. As will be seen later, if any rehauce can be put upon the 

 dextrose values, it is the dextrose which undergoes the greatest change 

 (see Fig. 3). This sugar appears to fall from 8 a.m. to 10 a.m., whilst 

 the starch increases; from 10 a.m. to noon the starch falls slightly and 

 the dextrose increases. From 12 to 2 p.m. the starch increases and the 

 dextrose falls ahnost to zero. After 2 p.m. the saccharose steadily 

 falls whilst the hexoses increase, apparently owing to the inversion of 

 the cane sugar, until 8 p.m. At the same time a sudden rise in the 

 starch occurs between 4 p.m. and G p.m. ; the starch which during the 

 earher part of the day had changed very little increases from 1-5 to 

 5-95 per cent. It is a striking fact that directly after the saccharose 

 reaches its maximum at 2 p.m. the "soluble starch" (or dextrin) can 

 be detected in the leaf material. This increases along a straight line 

 until a maximum is reached at 6 p.m. which corresponds with the 

 maximum of the starch. It is probable that the "soluble starch" is 

 formed as an intermediate product between the hexoses ( ? dextrose) 

 and the true, insoluble starch stored in the leaf. This form of starch 

 is only to be detected in the leaf between 2 p.m. and about 9 p.m., its 

 formation synchronising with the abnormally rapid increase of the starch, 

 which occurs 2 or 3 hours before sunset. In this particular case, the 

 starch stored in the leaf just before sunset is apparently very rapidly put 

 under contribution again, as it falls in amount to about 1-6 per cent, at 

 8 p.m. The rapid fall of hexoses from 1-2 to 0-4 per cent, between 8 p.m. 

 and 10 p.m. corresponds with a rise of starch from 1-6 to 2-6 per cent., 

 whilst the fall of starch from 10 p.m. to midnight corresponds with a 

 rise of hexoses. Between 12 midnight and 2 a.m. starch has almost 

 disappeared from the leaf (0-2 to 0-3 per cent.), but just before sunrise, 

 apparently in response to the first sign of daylight, the starch increases 



