W. A. Davis, A. J. Daish and G. C. Sawyer 277 



Saccharose and Reducing Sugars. The data given in Table I show 

 that, on the whole, there is a close agreement between the values obtained 

 for cane sugar by the two methods used — inversion by citric acid and 

 inversion by invertase. The values given are those obtained by the 

 reduction method; the results obtained by the double polarisation 

 method, as pointed out on p. 274, are uniformly higher. The cause of 

 this difference and of the fact that the reduction values obtained by 

 citric acid are nearly always slightly, but only slightly, higher than the 

 corresponding invertase figures, will be discussed in a separate paper. 



Fig. 4 shows that the cane sugar and hexoses both begin to increase 

 in amount immediately after sunrise ; the increase follows more or 

 less closely the temperature curve^. But whilst for the two sets of 

 sugars the increase from 6 a.m. to 10 a.m. takes place practically along 

 straight lines, this is not the case with the temperature, and the maxi- 

 mum of reducing sugar is reached at 10 a.m., considerably before the 

 maximum either of temperature or cane sugar; the maxima of these 

 last two curves however synchronise at about 2 p.m. During the period 

 of daylight the cane sugar curve is roughly parallel to the temperature 

 curve, the saccharose rising as the temperature rises and falling as the 

 temperature falls. On the other hand, the hexoses, which at first 

 increase more rapidly than the saccharose, subsequently, between 

 10 a.m. and 4 p.m., fall more abruptly than this sugar and during the 

 night period follow almost a straight line, which is very nearly parallel 

 to the straight line which shows the fall of the cane sugar. 



The important thing to be noted with regard to these curves is their 

 comparative simphcity as compared with the corresponding curves 

 later in the season (see Figs. 5 and 6). No night maximum is observed 



little staich in the loaf, show high concentration."! of sugars (compare Parkin [1912]). 

 As we sliow later, the potato, which forms starch abundantly, only contains a small propor- 

 tion of sugars in the leaf. 



The dependence of the starch content of the mangold leaf on the degree of development 

 is well shown by the results obtained on examining leaves of the mangold which were 

 plucked simultaneously on a bright day, at 11 a.m., July 15th, 1915, from plants growing 

 on differently manured plots. Leaves from plots 5 0, G 0, 8 0, which lack nitrogenous 

 manure, were very small, and contained an abundance of starch ; in all these cases the 

 root was still very small. On plot 2N (dung, super, potash and sodium nitrate) the leaves 

 were much larger (3 ins. x 2 ins.), but still showed some starch ; but on 2 A, where the leaves 

 were much farther advanced (5 ins. x 2J ins.) starch was practically absent. Even the 

 guard-cells of the stomata were nearly empty. 



^ We do not wish to infer that the increase is merely a temperature effect : the rise of 

 the sugars is probably directly related to th'' intensity of solar radiation and is a photo- 

 chemical effect of which the temperature gives merely a rough index. 



