EDIBLE CANNA IN WAIMEA DISTRICT OF HAWAII 33 
The small average weight of rootstocks in Group 1 during the 
months of June and July is due to the fact that the first rootstocks 
which become dormant are of the small cylindrical type. During 
the subsequent months the larger surface types pass over into Group 
1, thus giving rise to rapid increases in average weight until at the 
nineteenth month this value exceeds that of the other groups. 
A number of factors are to be considered in determining the proper 
age at which to harvest the canna crop: 
(1) The total yields continue to increase up to 19 months, and 
probably until the rootstocks of Group 1 ultimately rot, at which 
time the value would become constant. From the standpoint of 
total yield harvesting should be deferred until the dormant root- 
stocks begin to deteriorate, which usually takes place between 18 and 
24 months. Cultivation ceases after the first 6 or 7 months and the 
only expenditure for increase in yields after this period is for rental 
of the land occupied by the crop. 
(2) The manufacture of clean, white starch becomes increasingly 
difficult after the plants reach a certain stage. Even though the 
oldest rootstocks have not actually begun to rot they become watery 
and discolor quickly when opened, and the cortex becomes dry and 
corky. The surfaces of the rootstocks which have been broken by 
the action of the wind partly decay and exude sap which mixes with 
the soil and forms a hard mass. Although the starch granules ap- 
parently are not affected under such conditions, the discolored 
tissue and adhering soil interfere materially with the refining of the 
product. 
(3) As the hill grows beyond a certain stage, much of the younger 
growth of its rootstocks is small. This fact is not perceptible from a 
distance. The field may have a strong, vigorous top growth and 
stunted rootstocks. The latter may add considerably to the weight 
of the hill, but they are not desirable for starch manufacture. Not 
only do they increase the difficulties incident to washing but they 
are low in actual starch content. 
(4) In a previous bulletin (9) the starch content of a canna roots tock 
was shown to vary from 2.08 to 27.92 per cent, Group 3 containing the 
lowest. Obviously a field having a comparatively large part of its 
total weight in this group would yield less starch per ton of rootstocks 
than it would if this growth were allowed to reach the Group 2 
stage. In practice this point is hard to determine because of the 
prevalence in the field of new growth at all times. However, the 
relative proportion of Group 3 to the total weight of the hill decreases 
from approximately 50 per cent at 9 months to about 25 per cent at 
19 months. It is concluded, therefore, that the longer the hill 
remains in the ground the higher will be the proportionate yield of 
rootstocks of high starch content. 
Before the proper age at which to harvest the crop can be definitely 
determined experiments similar to the one undertaken will have to 
be repeated many times to take into account different seasons, times 
of planting, and soils. The available data seem to show that the 
crop should be allowed to grow until the new growth becomes of 
undesirable size, or until the dormant Group 1 gives signs of deteri- 
orating. In the foregoing experiment this would be between 17 
and 18 months. 
