THE ORGANIC ELEMENTS. 11 



as the so-called solution does not penetrate through cell-membranes. In 

 the plant it is ordinarily defended from this solution by the action of 

 wax, albumen, mucus, and the like. It is easily soluble (diffusible) in 

 boiling water, acids, and alkalies ; insoluble in alcohol, ether, volatile 

 and fixed oils, and is coloured blue by iodine in the most dilute solution.* 

 It appears, through modifications such as lichen-starch, to pass into amy- 

 loid, and, through the body discovered by Henry in mace, into cellulose 

 vegetable jelly, and perhaps also gum. On its chemical composition the 

 most distinguished chemists, Berzelius, Liebig, and others, are all agreed : 

 C 12, H 10, O 10. It forms the cell-wall in the asci of Lichens ; and in 

 some, as the Iceland moss (Cetraria islandica\ it is found in the external 

 layer of the thallus. It is also present, forming the contents of the cells. 



A. .The Nature of Potato Starch. 



The ordinary potato-starch of commerce consists of a somewhat coarse, 

 glistening, white powder, intermixed with larger pieces. On rubbing it 

 between the fingers, it pulverises more finely, but is somewhat hard to 

 the touch, and grates between the teeth. When moistened it cakes to- 

 gether in largermasses, and does not fall to pieces again on being re-dried. 

 When, however, this starch, after a long-continued extraction with cold 

 water, has been thoroughly purified with alcohol and ether, it forms an 

 extremely fine, glistening powder, which will not continue to adhere 

 together on being moistened and dried. Some considerable time is re- 

 quired to purify the starch perfectly, and the fluids used for its purifica- 

 tion continue for a long time to exhibit traces of albuminous matters and 

 of fats. The very various views that have been entertained regarding 

 the chemical relations of starch appear to me specially to arise from the 

 fact, that experiments are never made with perfectly pure, but with 

 variously adulterated, specimens. Payen and Persoz were the first who 

 seem to have thought of thoroughly purifying starch before they used it, 

 and the consequence was that the result of their experiments wholly 

 differed from those of others, and showed that starch was a perfectly 

 homogeneous vegetable substance. 



When magnified 100 times, the separate granules of starch appear like 

 small, solid, invariably ovate corpuscles. Deviations from this form are, 

 comparatively speaking, very rare. In starch that has been freshly 

 extracted from the potato, we recognise most distinctly a small black spot 

 by its pointed extremity : this is Fritsche's nucleus. It is only very 

 rarely, and when very strongly magnified, that it appears as a speck in 

 the potato, filled with such a thin substance as to allow of our regarding 

 it as an indentation, or rather as a small cavity, in the denser mass. This, 

 however, is made much more clearly evident in the starch extracted from 

 the bulbs of some of the Liliacece, and is established with perfect certainty 

 on comparing it with various other kinds of starch. Around this so- 

 called nucleus there appears, sometimes paler or blacker, or sometimes 

 closer or further, a large number of lines, which at first pass circularly 

 round the nucleus : further on they describe more of an oval course, as 

 they elliptically enclose the nucleus like a focus. The space enclosed 

 by two such lines appears sometimes lighter, sometimes darker, often 

 strikingly clear at separate spots ; and an experienced microscopic 

 observer will soon recognise layers of different density, and that the 



* Iodide of starch is not more soluble in water than starch, and insoluble in acids. 



