24 



The difference between the walls and the contents of the starch-grain probably 

 reposes on incrustation. We have namely to think the surface of the grain as con- 

 sisting of the albuminous matter of the amyloplast mixed with the secreted granulose 

 by which the thus formed mixture has become insoluble in boiling water. This would 

 be in accordance with the general observation, that incrusting substances highly 

 alter the solubility of bodies susceptible of imbibition, of which the lignified and 

 suberified cell-walls of plant cells and tanned leather are good examples. This con- 

 ception would lead to the conclusion that the amyloplast does originally incrust the 

 membrane of the starch-grain, but later draws back from it, wherewith the change 

 of amylocellulose (amylopectose) into granulose (amylose) would correspond. 



If this view is right the quantity of albuminous matter, which occurs in the 

 membrane, must be very small, for in the rate of nitrogen no distinct difference 

 between amylocellulose (amylopectose) and starch could be found, in both cases it 

 being about 5 milligrams per 100 grams of dry matter. 



Maquenne says that his amylopectose is not coloured by iodine ; the amylo- 

 cellulose (amylopectose) obtained from starch after extraction of the granulose 

 (amylose) in the manner here described, proves to colour violet blue with it. It is 

 not impossible that in this case, too, a kind of incrustation should occur, namely of 

 an adsorption of granulose in the amylocellulose wall, which then itself would in pure 

 condition remain uncoloured by iodine. 



All other species of starch examined by me behave in the same way as potato- 

 starch. 



