STARCH-GRAINS. 
6l 
from without inwards ; the extracted places are coloured copper-red by dilute iodine, 
the remaining mass blue; then the grain breaks up into pieces, which are finally 
completely dissolved (as in the endosperm of germinating wheat, Fig. 50, B). In 
other cases the solution begins also in particular spots of the circumference; the 
whole substance, however, gradually dissolves; holes are formed, and finally the 
grain breaks up into pieces (as in the maize, Fig. 50, ^). In the cotyledons of 
germinating beans, the solution of the 
ellipsoidal grains begins from within ; but 
before they break up into pieces, the 
granulöse is often so completely extracted 
that they assume with iodine a copper-red 
and in parts a bluish colour; afterwards 
the whole is dissolved. In germinating po- 
tatoes and the rhizome of Canna lanuginosa, 
on the other hand, the solution of the 
grains advances from without inwards, re- 
moving layer after layer. Probably this 
takes place when saliva is employed, 
whether the solvent acting slowly first ex- 
tracts the granulöse, or attacking it ener- 
getically dissolves the whole substance. 
Observations on embryos of the same 
species, germinating at different tempera- 
tures, would possibly show corresponding 
differences. 
(c) Solubility, Spelling. If starch-grains 
are crushed in cold water, a small portion 
of the granulöse is dissolved ; addition 
of iodine occasions precipitation of fine- 
grained blue pellicles^. Starch -grains 
ground with fine sand yield an actual 
solution of granulöse to cold water. Other 
fluids, as dilute acids, do not cause a solu- 
tion of the starch, but rather a trans- 
formation into other substances (dextrin, 
dextrose), which then dissolve. 
Water of at least 55° C. causes the 
swelling and conversion into paste of larger 
more watery starch - grains ; in smaller 
denser ones this begins, according to 
Nageli, at 65°. After heating in the dry 
state to about 200° C, subsequent moisten- 
ing causes swelhng; but the substance is by this means chemically changed; it is 
transformed into dextrin. In the production of paste, the interior watery parts swell 
first, the outermost layer scarcely at all ; it bursts and remains for a long time re- 
cognisable by iodine as a pellicle, even after the breaking up of the inner parts into 
small particles. A similar effect is caused by weak cold potash or soda solution ; the 
volume of a grain may thus be increased one hundred and twenty-five fold, and so 
much fluid be absorbed that the swollen grain contains only from 2 to o"5 per cent, of 
solid starch. 
Fig. so.- 
filled with 
A a cell of the endosperm of the 
crowded and therefore polyhedral starch-grains : between the 
grains lie thin plates of dried-up fine-grained protoplasm ; small 
cavities and fissures are formed in the interior of the grains by 
drying ; a—^r starch-grains from the endosperm of a germi- 
nating seed of maize ; B lenticular starch-grains from the 
endosperm of a germinating seed of wheat ; the commencing 
of the action of the solvent is shown by the more evident ap- 
pearance of stratification (X 800). 
^ On the actual solubility of starch, see the remarks in my Handbuch der Experimental 
Physiologie, p. 410. . ' 
