W. A. Davis, A. J. Daish and G. C. Sawyer :]05 



The same is true of the snowdrop, studied by Parkin, which stores 

 starch and iuuhn. 



The relatively high proportion of cane sugar in the mangold leaf 

 during the early stages of growth^, as well as the experiments recorded 

 by Parkin ([1912], p. 31) showing the enormous increase of the cane 

 sugar which occurs in the leaf of the snowdrop when plants previously 

 kept in darkness for 4 days are exposed to light, support the view that 

 saccharose is actually a direct product of photosynthesis. In Parkin's 

 experiments the cane sugar increased 2| fold, whilst the hexoses only 

 increased by one-third. It is probable that in the mesophyll of the 

 leaf, saccharose is the sole sugar present, and the invert sugar is first 

 formed in the veins or small vessels which serve as conducting channels 

 to the mid-ribs. Our analyses of course could only be made with leaf 

 tissue from which the largest conducting vessels were removed (viz. 

 the mid-ribs), but the tissue actually worked with still contained all the 

 smaller vessels and it was probably in these that the small proportion 

 of reducing sugars found in the early stages of growth was located. 



One of the most striking features of the stalks and mid-ribs is that 

 the proportion of saccharose remains practically constant throughout the 

 whole 24 hours, whilst the hexoses fluctuate between wide limits (see 

 Figs. 7 to 10). Thus in Series I, for example, the cane sugar in the tops 

 of the stalks varied only from 3-75 to 4-39 per cent., whilst the hexoses 

 had a range of from 5-35 to 13-17 per cent. Moreover, whilst the 

 percentages of reducing sugars in the top and bottom halves are widely 

 different at any one time, the bottom half always being the richer, the 

 proportion of saccharose in the two halves is practically the same. 

 Thus, for example, at noon (Table V) when the invert sugar in the top 

 half was 9-97 per cent, and in the bottom half 13-17 per cent., the cane 

 sugar in the top half was 4-39 and in the bottom half 4-12 per cent. 

 As the season advances the proportion of cane sugar at corresponding 

 times of day changes but little, whereas the hexoses increase enormously. 

 For example, we may take the following: 



' The predominance of cane sugar in the leaf in the early stages of growth points to 

 the rate of production of this sugar exceeding the rate of its hydrolysis by invertase; 

 the fact that during the morning the hexoses (see Fig. 4) increase faster than the cane 

 sugar poults to the hydroljrtic effect of the enzyme increasing more rapidly with rise of 

 temperature (or an actual increase in the amount of enzyme occurring) than the synthetic 



effect producing the saccharose. Tlie parallelism of the curve showing the ratio — — 



witli the temperature curve in fjoth Series I and II is best explained in this way. 



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