STAKCH-SUBSTANCE, AND THE STRUCTURE, ETC., OP THE STARCH-GRAIN. 21 



if starch be rubbed for a period of half an hour in a mortar with double the volume of 

 water, there is formed a viscid, stiff "salve," capable of being drawn into threads. A large 

 number of the granules when seen under the microscope appeared to be crushed in various 

 ways, and partly ground into small flakes. The inner layers are combined with more water 

 by friction, exhibiting a finely floccular or granular but connected mass, which is colored 

 blue with iodine, while all the water surrounding the mass remains wholly uncolored. 

 On heating the grains upon a small plate he observed that one can trace gradual changes 

 brought about by heating, and that thus may be found the best explanation of the struc- 

 ture of the grains. The first action is one of drying, by which the so-called nucleus or 

 hilum is converted into an air-bubble. The several layers separate simultaneously, and 

 in consequence of inspissation the lines of separation become sharper, darker, and broader, 

 and also even recognizable broader and narrower layers of air, the layers hanging closer 

 together at some places than at others. By degrees the separate layers peel away from 

 each other like the scales of a bulb. If the grains are boiled in water their outlines grow 

 more and more distinct, but the particles cling together in the form of a paste-like mass. 

 Under the microscope, by means of iodine, he found that we may recognize the separate 

 and swollen granules, while the water added is never colored blue. He believes from these 

 phenomena that while starch may take up a large ciuantity of water, it can never be properly 

 dissolved. The layers of the starch-grain he regards as being more aqueous as they lie 

 further inward. By testing with iodine he noted that all parts of the grain are stained 

 equally, and that while there may be slight differences in the external layers in relation 

 to solvents, differences which he believes arise from the adhesion or infiltration of traces 

 of albumin, fat, or wax, such differences merely delay the action of the solvents. 



Schleiden studied the phenomena of erosion and formation of the grains in the potato. 

 During erosion the grains retained theh- solidity to the last moment, and were only gradually 

 attacked from the exterior inward, the extremities of the longitudinal sections offering 

 the greatest resistance, on which account the grains after a time resembled knotty twigs. 

 In young growing potatoes he found exceedingly minute granules and large grains, the 

 former being the more numerous. He states that if we regard the minute granules as the 

 rudiments of structure, and take the different sizes as indexes of their age, the younger 

 the granules the more truly spherical they appear, the ovoid or irregular outline being 

 subsequently acquu'ed, and the deviations from the original form being caused by the 

 unequal thickness of the outer layers. The innermost layers continue to exhibit the 

 original spherical form which the youngest granules present. Starch therefore grows, he 

 concludes, by the deposition of outer new layers upon the inner older layers. This he 

 found confirmed when starches from the other plants were compared with grains from the 

 potato, as, for instance, grains from Dieffenhachia seguine. Sclileiden also noted that the 

 forms of starch-grains are exceedingly various, and he made a tabular list of grains from 

 various sources based upon histological peculiarities (see page 64). 



The view that starch-grains grow by the external apposition of layers was asserted 

 by Walpers (Botanische Zeitung, 1851, ix, 329) to be disproved by the fact that in twin 

 grains, which occur so abundantly, the hila are not located near the line of fusion of the 

 component grains, but always near the circumference; and that the formation of "be- 

 tween-layers " which takes place at the line of contact is not explained by deposition of 

 layers from without. The theory of external apposition he states is contradicted by the 

 fact or assumption that the most outer layer is the oldest, and the layers within the 

 youngest, in succession from periphery to center. The outer layers he states are usually 

 the densest, yet they must be thin to be able to stretch to attain the maximum size of the 

 grain. Walpers holds that to adjust such an indisputable contradiction, two possible 

 answers present themselves: (1) the outer older layers grow simultaneously with the 

 growth of the interior, which can not be the case, because the lamellation indicates an 



