:J()() The Cdrhuhydrafrs of the M>iii(/<>/(f Leaf 



It is a striking fact (compare Table V with Table VI and the data for 

 mid-ribs and stalks in Table \'III) that the proportion of saccharose 

 in the mid-ribs (which are nearer the leaf tissue) is slightly higher and 

 somewiiat less constant than in the stalks. For example, in Series II : 



In stalks, saccharose varies from 4-82-5-2G per cent. ; hexoses from 

 20-5-26-7 per cent. 



In mid-rihs. saccharose varies from 6-OS-7-44 per cent.; hexoses 

 from 19-0-23-6 per cent. 



On passing from the stalks, through the mid-ribs to the leaves, the 

 range of variation of the saccharose during the day increases, but even 

 in the leaves the variation of cane sugar during the daytime is far less 

 marked than that of the hexoses. Parkin also observed in the snowdrop 

 a similar phenomenon (loc. cii., p. 28) as regards the seasonal variation, 

 but the fluctuation of the hexoses between morning and evening was less 

 marked than that of the saccharose [loc. cit., p. 29). This was probably 

 due to the fact that he took only two samples in the day, one at a 

 time when the sugars were increasing, the other when they were falling. 

 A similar false conclusion as to the approximate constancy of the 

 hexoses and wide variation of the saccharose would be formed if samples 

 had been taken in Series III (Fig. 6) at 9 a.m. and 3 p.m. only, but the 

 general shape of the curves in Series I and II shows that during the 

 period of daylight the hexose is the more variable even in the leaf. 



The great variation during the day of the reducing sugars and the 

 practical constancy of the cane sugar in the mid-ribs and stalks, and 

 the fact that the proportion of cane sugar in the top and bottom halves 

 of the stalks is practically the same, point to the relatively rapid move- 

 ment or formation of the hexoses in the mid-ribs and stalks. In the 

 case of the snowdrop, Parkin (loc. cit., p. 25) foimd that the long, narrow 

 leaves contained a far larger proportion of hexose to cane sugar in the 

 upper parts than in the lower parts, especially when the plants were 

 grown in clumps so that the lower parts were shaded ; in this case, the 

 lower halves of the leaves functioned mainly as stalks or media of trans- 

 location not as true assimilating leaves, the results presenting an exact 

 parallel with those obtained in the case of the mangold stalks. Parkin 

 also found that the colourless part of the snowdrop leaf which is enclosed 

 by the membranous sheath is verv rich in sugar — 30 to 40 ])er cent, of its 



