STARCH-GRAINS. 



61 



I from without inwards ; the extracted places are coloured copper-red by dilute iodine, 

 Ihe 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, A). In the cotyledons of 

 germinating beans, the solution of the 

 ellipsoidal grains begins from within; but 

 before they break up into pieces, the 

 granulose 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 granulose, 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, Snivelling. If starch-grains 

 lare crushed in cold water, a small portion 

 »f the granulose is dissolved ; addition 

 >f iodine occasions precipitation of fine- 

 'grained blue pellicles^. Starch -grains 

 ground with fine sand yield an actual 

 solution of granulose 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° G. 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 swelling; 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 0-5 per cent, of 

 solid starch. 



Fig. 50. — yi a cell of the endosperm of the maize, filled with 

 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 grahis by 

 drying ; a^£- 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 

 lysiologie, p. 410. 



