STARCH-SUBSTANCE, AND THE STRUCTURE, ETC., OP THE STARCH-GRAIN. 39 



ceives takes place in a tangential direction only. The tendency of the grain is to increase 

 constantly on its periphery, but this is liindered l)y the inner expanding lamelhe. Thus 

 there is a positive tension between every lamella and the next inner lamella, and a negative 

 tension between it and the next outer lamella. 



Strictly speaking, Strasburger states, only in centric starch-grains does the water- 

 content of the lamelliB increase from without inward. In eccentric grains the increasing 

 water-content of the lamellae applies only to the oldest central parts of the grain. The 

 greater density of the surface is due to the lower water-content. The influence of the sur- 

 rounding medium lowers the swelling capacity of the surface, and it also gives rise to the 

 following phenomenon noted by Harting: By contact with water there very often form den- 

 ticular projections which are caused by a more rapid swelling of the layers closely packed 

 below the surface, whereby the surface-membrane becomes turned over at some places. 



Strasburger notes that by cutting or crusliing starch-grains swelling is increased because 

 of the greater or less disorganization. Cohesion in starch-grains is feeblest in a tangential 

 direction, and tension relations are therefore equahzed by means of radial cracks. In 

 concentric grains the innermost and most watery layer and the hilum lose most water in 

 drying, and hence the cracks center at the hilum. The adhesion of the lamella? is stated 

 to be ^■ery great, so that the layers can not be separated by means of pressure, while the 

 formation of radial cracks is easily accomplished by pressure. Strasburger writes that the 

 radial structure of starch-grains suggests the conception that the rod-like elements of the 

 grains are crystal needles arranged radially. 



The component of raw starch that is soluble in cold water was studied by Bruckner 

 (Monatschefte f. Chemie, 1883, iv, 889) and identified with the amidulin described by 

 Nasse (Inaug. Dissert. Halle, 1860) and with the granulose of C. Nageli. Bruckner diied 

 the grains and crushed them between glass plates, causing many cracks. After macera- 

 tion in water, and repeated filtering, a filtrate was obtained which became blue upon the 

 addition of iodine. In another experiment, the whole grains (Zea) were placed with three 

 volumes of water in a cylinder and set aside for three weeks, duiing which period the 

 mixture was shaken daily. At the end of this time the preparation was filtered, and the 

 filtrate was evaporated to one-fifth of its original volume. No trace of a blue reaction 

 with iodine was obtained. From these results, Bruckner concludes that the outer firm 

 layers or coats serve as a protective membrane to the inner layers, and that the soluble 

 starch can be extracted by cold water only after cutting, breaking, or otherwise injuring 

 the outer layers, and thus exposing the inner soluble portion. 



Shubert (Monatschefte f. Chemie, 1884, 472; Jour. Soc. Chem. Ind., 1885, iv, 236) 

 investigated the behavior of starch-granules on being heated, and concluded that changes 

 in form and structure, especially the lamination, are not solely deterinined by the amount 

 of moisture in the air-ch'ied granules, but depend also on the different physical and chemical 

 properties of each layer. The effect of heat was found sufficient to make these differences 

 more prominent. The starch-granule, under the influence of high temperature, is altered 

 in such a manner that the layers that are rich in granulose are at once converted into solu- 

 ble starch and dextrin, while the principal portion of the layers that are rich in cellulose 

 undergoes this transformation only after a time. When starch wliich has been heated is 

 treated with water of the ordinary temperature, the soluble starch and dextrin are removed 

 and an organized residuum is left, wliich resembles the form and structure of the original 

 granule and contains small quantities of unchanged granulose. This granulose can be 

 further removed by extracting with water, and it appears to be in such a state as to be 

 readily changed in its chemical projierties. The grains give up the greater portion of the 

 granulose to the water, thereby losing in mass but not in volume, retaining their structure, 

 the residue consisting chiefly of cellulose. Grains extracted in this way become colored blue, 

 or, at least, bluish-violet, on the addition of sulphuric acid and iodine, and the individual 



