W. A. Davis, A. J. Daish and G. C. Sawyer 281 



practically identical in form. In Fig. 4 the rise and fall of matter insol- 

 uble in alcohol which occurs just before and after dark (6 p.m. to 

 10 p.m.) is accompanied by a corresponding rise and fall of pentosan ; 

 the increase of pentosan at this point seems to be associated with the 

 sudden falling off of free pentoses, which occurs between 6 and 8 p.m., 

 but the pentoses subsequently rise during the night, side by side with 

 the rise of pentosans and of matter insoluble in alcohol. 



The increase in the amount of pentosan and of matter insoluble in 

 alcohol which is visible during the day in spite of the increase in the 

 amount of substances soluble in alcohol is partly due to the formation of 

 new ligneous tissue, but is probably more the result of the formation of 

 gummy substances, which we have found always to be present in 

 considerable quantity in the leaf tissue. These gums, as we shall show 

 later, probably play the part of reserve substances (see p. 285). 



Although the pentosan does not vary within very wide limits (5-2 to 

 5-96 per cent.), the value at the end of the 24 hours (5-96) is considerably 

 higher than at the commencement (5-38) ; a similar but even larger 

 increase is found at the September picking (see Table II and Fig. 5). 

 This is probably due to the increase of the ligneous constituents of the 

 leaf. In October when the pentosan has increased to about 7 per cent., 

 and the leaves are no longer growing, there is very little variation 

 during the day (6-89 to 7-15) other than can be accounted for by the 

 much wider variations of the total sugars. 



Pentoses. Between 6 a.m. and 4 p.m. there is a slight rise in the 

 pentoses, followed by a slight fall, the curve running more or less parallel 

 with the other sugar curves. Between 4 p.m. and 8 p.m. there is an 

 abrupt rise of the pentose followed by an abrupt fall, these changes 

 synchronising with a fall and a rise respectively of pentosan. During 

 the night the pentose rises fairly steadily, and the same is true of the 

 pentosan, both changes apparently taking place at the expense of the 

 saccharose and reducing sugars, which are falhng steadily throughout 

 the night — especially the hexoses, which practically disappear. These 

 facts and the parallelism of the pentose curves with those of the other 

 sugars during the day, suggest that the pentoses arise from the reducing 

 sugars and the pentosans from the pentoses. 



At this stage of growth, when leaf formation is predominant, it is 

 interesting to note that the pentoses (0-41 per cent.) at their midday 

 maximum have roughly the same ratio to the pentosan tissue (5-5 per 

 cent.) as the other sugars (5-2 per cent.) have to the total insoluble leaf 

 material (60 per cent.), the ratio being roughly yV. 



