378 
LEWIS KNUDSON 
the writer has found that the root-cap cells that accumulate at the bottom 
of the culture flasks are not dead but apparently remain alive for a very 
considerable period. Examination of the sloughed off root-cap cells at 
the conclusion of the experiments revealed that they were alive and in good 
condition. Furthermore, the total weight of such cells would not be over 
20 milligrams. 
It seems to the writer that there is only one explanation to account for 
the accumulation of reducing sugars, and that is excretion of reducing 
sugars by the roots. 
In accordance with this view, the procedure might be as follows : Sucrose 
is absorbed by the roots and inverted in the root cells by the enzyme inver- 
tase. Some of the sugar is used in growth, but there is a superabundance 
of reducing sugars and they accumulate in the root cells. At the outset 
there are practically no reducing sugars in the sucrose solutions. The 
concentration gradient between the reducing sugars in the cells and those 
outside is steep, and consequently some of the reducing sugars diffuse 
outward. With the progress of time the difference in concentration of 
reducing sugars becomes less, but probably it is considerable at all times, 
since at the conclusion of the experiment the concentration of the sucrose in 
the culture is much greater than that of the reducing sugars; and since there 
is a constant inward diffusion of sucrose, there results a constant production 
of reducing sugars in the plant cells. 
In support of the view that the reducing sugars are excreted, the following 
experiment may be cited. Three corn plants which had grown for 30 days in 
Pfeffer's solution, each plant having a fresh weight of approximately 18 
grams, were removed from the culture vessels and the roots washed in tap 
water. At 5 p.m. the plants were transferred to culture vessels so that 
their roots alone were bathed in a four percent solution of sucrose (Merck's 
highest purity). Three culture vessels were used and 400 cc. of the solution. 
The roots were kept in this solution for 16 hours. The plants were then 
removed and rinsed seven times in tap water, and then the plants were 
transferred to culture vessels this time containing distilled water. The 
plant roots remained in distilled water 7 hours. The total volume of 
distilled water was then reduced by evaporation to 100 cc. This was 
analyzed for reducing sugar and the determinations gave 14.5 milligrams of 
reducing sugar. 
In another experiment plants were used which had been growing in a 
nutrient solution plus sucrose, and treated in the same way as in the pre- 
ceding experiment. There were leached from the roots of four plants 
75 milligrams of reducing sugar and 150 milligrams of sucrose. 
The secretion of sugars by the roots of plants may seem at the outset to 
be a rather startling idea, yet theoretically there is no reason why this 
should not occur. Wachter (9) reported considerable excretion of sugars 
by slices of beets and onions when immersed in distilled water or in salt 
