STARCH GRAINS. 



61 



temperature suffices for wheat-starch, a higher is required for that of the potato. Nageli 

 gives in general 4o°-47° G. 2. According to Melsens a similar extraction may also 

 be effected by organic acids, diastase, and pepsin. 3. According to Nageli it can be 

 accomplished also by very slow action of hydrochloric or sulphuric acid which has been 

 so diluted with water that it does not cause the starch-grains to swell. 4. According to 

 Franz Schulze, the granulose is extracted by a saturated solution of sodium chloride 

 containing i p. c. of concentrated hydrochloric acid, at 60'' C. in two to four days ; the 

 residuum, which does not perfectly show the organisation of the starch-grain, amounted, 

 according to Dragendorff, to 5*7 p. c. in potato-starch, 2*3 p. c. in wheat-starch. These 

 skeletons are not at all coloured by iodine (Nageli's preparation with sulphuric acid after 

 one and a quarter year's extraction), or 

 they become copper-red, and in places 

 where the extraction was not perfect, 

 bluish. They do not swell in boiling water. 

 At 70° C. the whole starch-grain, according 

 to Mohl, is dissolved in saliva : the ske- 

 leton produced at 40°-55° G. is, however, 

 not affected by saliva at 70°. 



Within the living cell the starch may 

 be dissolved in very different ways ; pro- 

 bably solution occurs mostly under the in- 

 fluence of protoplasm or by the assistance of 

 nitrogenous combinations in the cell-sap. 

 Sometimes the solution begins, as in 

 the extractions mentioned above, with the 

 removal of the granulose, the cellulose re- 

 maining behind ; but this often takes place 

 only partially ; the extraction proceeds in 

 single places from without inwards ; the ex- 

 tracted places are coloured copper-red by 

 aqueous iodine, the remaining mass blue ; 

 then the grain breaks up into pieces, which 

 finally are completely dissolved (as in the 

 endosperm of germinating wheat, Fig. 52, 5). 

 In other cases the solution begins also in 

 particular places of the circumference ; 

 the whole substance, however, gradually 

 dissolves ; holes are formed, and finally 

 the grain in these cases also breaks up 

 into pieces (Zea Mais, Fig. 52, A). In the 

 cotyledons of germinating beans, the so- 

 lution 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 potatoes and the root-stock of 

 Canna lanuginosa, on the other hand, the solution of the grains proceeds from without 

 inwards, removing layer after layer. Probably the same takes place here as when 

 saliva is employed, whether the solvent acting slowly first extracts the granulose, or 

 attacking it energetically dissolves the whole substance. Observations on germinating 

 plants of the same species, developed at different temperatures, would possibly show 

 corresponding differences. 



(c) Solubility, Snivelling. If grains of starch are crushed in cold water, a small 



Fig. 52. — A a cell of the endosperm of Zea Mai's, filled with 

 crowded and therefore polygonal starch-grains : between the 

 grains lie thin plates of dried fine-grained protoplasm ; small 

 cavities and fissures are formed in the interior of the grains by 

 drying ; a— ^ grains of starch from the endosperm of a germi- 

 nating seed of maize ; B grains of starch (lenticular) from the 

 endosperm of a germinating seed of wheat ; the commence- 

 ment of the action of the solvent is shown by the more evi- 

 dent appearance of stratification (x8oo). 



