BULLETIN 56, HAWAII EXPERIMENT STATION 
The storage organ or lower part of the plant is essentially a root- 
stock, or part of the stem in which starch is stored, and morphologi- 
cally it is an integral part of the stem. In some of the types of slender 
rootstock it is difficult to determine just where the rootstock ends 
and the stem proper begins. 
Under normal conditions the new rootstocks attain very consider- 
able size with energy supplied by the parent plant, their own stems 
remaining entirely undeveloped. (Figs. 1 , 3, 4, 5, 6, and 7 ) When vig- 
orous growth of the meristem 
decreases, the internodes at 
the apex shorten very rap- 
idly, and the stem develops. 
Under optimum conditions, 
the rootstock continues to 
increase in size for some time, 
as is shown by the large, fresh 
cracks on its surface. In- 
crease in size, however, may 
be the result of cell elongation 
rather than of cell growth. 
The potency of the parent 
stem is strikingly shown by 
the fact that when all the ma- 
ture top is removed the hill 
produces extremely stunted 
rootstocks. (Fig. 8.) 
The first generation root- 
stocks are always small and 
cylindrical in type; the sec- 
ond, and sometimes the third 
generation, termed the inter- 
mediate type, have a definite 
tapering shape. They grow 
below the surface of the 
ground, starting with a small 
attachment to the parent, 
and increase in diameter to a 
definite bulge approaching 
the apex. The third and 
fourth generations, under 
ordinary cultural methods, 
grow at or near the surface 
of the ground, starting with a 
large attachment to the par- 
ent. They are oval to spher- 
ical and largely develop above 
the surface of the ground. 
(Fig. 3.) Subsequent gener- 
ations are of thissame 
general surface type. 
The characteristic shapes (fig. 9) may be attributed largely to the 
number of antecedent stems upon which the developing rootstock 
has to draw. The first generation has none The second generation, 
which closely follows the first, receives little plant food from the par- 
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Fig. 1.— A hill of canna, 6 months old, at its maximum 
growing stage. The stems of the first three generations 
have bloomed and are functioning at their maximum 
in producing sugars for the stoiage of starch and for the 
production of new growth. Note the large, vigorous 
new rootstocks 
