CARBOHYDRATE METABOLISM AND GROWTH IN EDIBLE CANNA H 
If the specific gravity and starch content of the several hills are 
plotted as separate curves (fig. 14), each hill would seem to have 
what might be termed a characteristic "growth curve," the location 
and nature of which depends upon a number of factors, including age, 
rainfall, and rapidity of growth. 
The curve of hill S, from Waimea rootstocks, covering a wide range 
of percentages and lying about midway of the curves of hills A and B, 
was adopted for field studies and mill control. Table 5, taken from 
the curve of hill S, shows the approximate starch content of root- 
stocks as ascertained by the specific gravity. 
Table 5. — The starch content of rootstocks as determined by specific gravity 
Specific 
Starch in 
Specific 
Starch in 
Specific 
Starch in 
gravity 
rootstock 
gravity 
rootstock 
gravity 
rootstock 
Per cent 
Per cent 
Per cent 
0.98 
3.5 
1.03 
10.2 
1.08 
18.7 
.99 
4.7 
1.04 
11.7 
1.09 
20.9 
1.00 
6.0 
1.05 
13.3 
1.10 
23.3 
1.01 
7.4 
1.06 
15.0 
1.11 
26.1 
1.02 
8.8 
1.07 
16.8 
1.12 
30.3 
Determination of the starch content of a rootstock by its specific 
gravity is admittedly only approximate. The only varying factors 
considered are starch and water; differences in structure or of air 
spaces within the rootstock are not taken into account. The latter, 
particularly, introduces appreciable error in the determination. The 
specific gravity of a canna rootstock may be increased from 1.07 to 
1.12 and higher by placing the rootstock in water and evacuating. 
Notwithstanding these imperfections the method has much practical 
value in both field and factory. Obviously, its accuracy depends 
upon the number of analyses from which the table is constructed, 
and many additional analyses will have to be made before a thor- 
oughly reliable table can be made. 
CARBOHYDRATE METABOLISM 
Variations in the sugars of the sap of the canna plant offer special 
advantages to the chemist in studying its methods of growth as a 
starch crop. The relationship between the sugars and the growth of 
the plant can be learned, as well as the various changes taking place 
in form and concentration of the sugars during translocation and ulti- 
mate storage as starch. 
Study of the occurrence of sugars in the metabolism of the plant 
and their significance began with the discovery by Sachs (12) in 1862 
of starch in the chlorophyll-granule and his conclusion that starch 
disappears from the leaf by conversion into sugar. Schimper (13) 
modified Sach's hypotheses by stating that glucose formation precedes 
starch formation in the leaf, and that starch is formed from glucose 
when its concentration exceeds a certain maximum, which varies in 
different plants. 
Meyer (10) observed that the leaves of many plants contain no 
starch, and that such leaves usually have a high sugar concentration 
compared with those containing starch. Later, Brown and Morris 
(2), using more exact chemical methods, studied the nature of the 
