THE VEGETABLE CELL. 45 



by Fritzsche in " Poggend, Ann." part 32 ; of Payen in ''Mem. 

 sur les Develojypements des Vcgetaux^'" and of Schleiden in. his 

 " Grundzhge!') 



The starch granules of different shape agree in the 

 circumstance that they are not composed of one uni- ^'^iJ- ^^• 

 form mass, hut of super-imposed layers of varying 

 density, whence they derive a pretty appearance with 

 polarized light, each granule exhibiting a coloured 

 cross. These layers are usually much thicker on one 

 side of the granule than on the other (fig. 4i6), so that 

 the organic centre is far removed from the middle 

 point, and often closely approximated to the surface. 

 In fresh granules there is no cavity in the centre, but ^*^the fSato! ^^ 

 one is readily produced by dessication and by the 

 contraction this produces of the internal softer substances. This 

 process may be traced very beautifully under the microscope, by 

 removing a part of the water, by strong alcohol, from fresh starch 

 granules taken from the Potato. In this case a little globular 

 cavity is first formed, and then radiating fissures soon run out in 

 all directions, traversing the layers of the granule at right angles. 

 This undoubtedly results from the middle layers being softer, and 

 more swollen up by water than the outer. But the firmness is 

 still so great that the starch granules may be broken up into 

 angular pieces by pressure. Cold water does not exert any sol- 

 vent power over them, even when the granules are cut into thin 

 slices, so as to allow the water to come immediately in contact 

 with their inner layers. In boiling water they swell very much, 

 even a hundred times their original volume, without actual solu- 

 tion. The same effect is produced by the action of strong acids 

 and caustic alkalies. When iodine and water act simultaneously 

 either in the swollen or unswoUen granules, these are coloured, 

 according to the amount of iodine they absorb, wine-red, indigo- 

 blue, and up to the deepest black blue, without undergoing any 

 alteration, for when the iodine is removed again by alcohol, they 

 again possess their original properties. 



In all vegetable cells starch is a transitory product, destined to 

 be re-dissolved at a later period, and applied to various purposes 

 of nutrition. Thus the starch disappears from the albumen of the 

 seeds of Palms about the period of maturation, and in its place 

 appears a fixed oil, for which it undoubtedly furnishes the mate- 

 rial ; thus it disappears in the elaters of the Liverworts when the 

 spiral fibre is developed in them ; and it vanishes during the ger- 

 mination of seeds and bulbs, serving for the nutriment of the 

 young plants, &c. It is unknown at present in what way the 

 solution of the starch granules takes place in these cases ; when 

 artificially converted into dextrine and sugar, by diastase or sul- 

 phuric acid, a swelling up of the granules precedes its transforma- 

 tion ; but this does not happen in the living plant, for the sub- 



