274 The Carbohydratei^ of the Mangold Leaf 



B. Error of sampling. The leaves of the mangold on different plants 

 at any particular date are very variable in size so that some doubt 

 might be felt as to tlie range of variation of the sugars due to differences 

 of sampUng. Our practice has been to pick about 120 medium-sized 

 leaves from the plot dealt with, ignoring the very large and very small 

 leaves. In all cases care was taken to choose leaves of a good colour 

 and normal growth, well exposed to light; one leaf only has been taken 

 from each root at eacli picking. To obtain an idea of the probable 

 extreme error of sampling under these conditions, two lots of leaves 

 were picked at precisely the same time (2.4-5 p.m., October 8th, 1914) 

 from the same plot, at a late stage of growth when the difference 

 between individual plants is at its greatest. These, on analysis, gave 

 the following results : 



Whilst there is a very close agreement (7-52 and 7-57 per cent.) for the 

 two samples in the case of cane sugar estimated by the change of reducing 

 power on inversion, tiiere is a considerably greater difference between 

 the values for reducing sugars, calculated as invert sugar; the difference 

 is about a single unit or about per cent, of the total reducing sugars. 

 The values obtained for saccharose from the change of rotation on inver- 

 sion are, as is usually the case, from 7 to 15 per cent, higher than the 

 reduction values ; no closer agreement is obtained by taking the initial 

 direct reading after saturating the solution with sulphur dioxide so as 

 to have it acid and not faintly alkaline, in fact the difference is slightly 

 greater. The cause of this difference is dealt with in the next paper. 



The above case probably gives an extreme value for the error of 

 sampling, as owing to the very dry autumn the leaves of most of the 

 plants were beginning to turn yellow and were far more variable than 

 is usual at this time of year, so that it was difficult to get a fair and 

 representative sample. The mangolds were lifted about three weeks 

 earlier than usual and this picking was made four days before the lifting 



