144 STARCHES, 



three classes : — (i) Those who considered the granule to be com- 

 posed of layers rolled, so to speak, over each other. 



(2) Those who considered it to be a vesicle increasing by 

 inward growth, the vesicle continually expanding up to a certain 

 point to allow of further internal increase. On this supposition 

 the internal layers would be the younger and the external the 

 elder. This view was strongly supported by AUman, as he found 

 the internal portion more easily attacked by such re-agents as sul- 

 phuric acid, acetic acid, and iodine, than the external. 



(3) Schlieden and Criiger, however, from identical experiments 

 connected with observations on compound starch granules, which 

 contained two or three hilums or centres of growth, came to the 

 opposite conclusion — namely, that the external layers were depo- 

 sited later than the internal, all with the exception of the nucleus 

 being chemically identical. 



Nagelli was of opinion that starch grains are utricles, consisting 

 of a membrane and fluid contents, concentric layers being depo- 

 sited on the inside of the membrane as in lignifying cells j the 

 cavity of the utricle, the so-called " nucleus " or " hilum," thus 

 becoming reduced to a most minute excavation always filled with 

 fluid. When starch is first treated with iodine, and then imme- 

 diately with sulphuric acid, the granule swells up and the lamellae 

 generally separate from each other. This experiment may be 

 made by any one possessing a microscope. 



From the latest observations of Sach and others, starch would 

 appear to be actually produced by the deposition or rather precipi- 

 tation of minute starch particles, which, cohering to each other, 

 gradually form the granule, the growth of the grain being produced 

 entirely by intussusception — i.e.^ by the intercalation of new par- 

 ticles amongst those already deposited. This mode of growth 

 necessarily depends on the permeability of all parts of the grain 

 to the aqueous solutions, from which starch particles are precipi- 

 tated. This again can only be explained by supposing the starch 

 substance to be discontinuous, consisting of minute, invisible par- 

 ticles, each of which possesses the power of attracting moisture 

 and enveloping itself with an aqueous envelope. 



Where the particles are large, the number of these aqueous 

 envelopes in a given bulk of starch will be less than when the 



