36 STARCH GRAINS. 



2nd. That it is a solid body, constituted by layers one upon the other, beginning 

 either -within (centripetal), or without (centrifugal). 



On the first of these theories the markings upon the surface are produced by the 

 folding of the cell-wall ; and on the second, by the successive layers of the solid starch. 



Leeuwenhoeck, a celebrated microscopist, published certain investigations made 

 by him nearly a century and a-half ago, in which he showed the cellular character 

 of starch. Since his era many eminent observers have adopted his views, with 

 certain modifications ; and very recently two, whose experiments we shall describe, 

 viz , M. Martin, the librarian of the Imperial Polytechnic Institute at Yienna, 

 and Mr, Busk, a distinguished naval surgeon and microscopist. Both these gen- 

 tlemen agree in the theory of the constitution of the starch granule m., that it is a 

 cell, having a cell-wall much larger than the contents of the cell in the dried state, 

 and, therefore, puckered and plaited, as indicated by the lines upon the surface. M. 

 Martin says, that "the primary form of the starch grain is a spherical or ovate cell. If 

 this be considered as empty, and so contracted that one-half lies in the other half, a 

 watch-glassrshaped basin is formed, which, after boiling and pressure between two 

 glasses, appears, in consequence of the delicacy and elasticity of the membrane, as a 

 flat, round^edged disc." Thus, in his opinion, the ovate cell is inrolled upon itself. 



Mr. Busk has not satisfied himself in reference to this unfolding of the membrane, 

 but thinks that the swelling up of the cell by the addition of strong sulphuric acid 

 rather indicates the distinction of plaits or folds, and more particularly in such 

 varieties of starch as have, when dried, a puckered centre, as is exhibited in Figs. 78 /, 

 and 80. As this is a most interesting and undetermined question, and one, more- 

 over, which our intelligent readers who have microscopes may be desirous to investi- 

 gate, we subjoin the methods adopted by the observers just mentioned. 



In any examination of starch it is only necessary to take a pin's point of flour of 

 wheat, or of some other grain, or to scrape a very little morsel from the cut surface of 

 a potato, and in both cases the starch will be found partly in free grains and partly 

 inclosed as masses of grain within the cellular tissue of the plant. 



The grains of Tous Us Mois (Fig. 78 /) are the largest, and therefore, in many re- 

 spects, the most convenient for examination ; as also those of the horse-chestnut (Fig. 

 79), and pea (Fig. 78 ), when it is desired to notice the unfolding of the central 

 puckerings. 



M. Martin's method was as follows : " Between two very thin glasses, of the same 

 size as the stage of the microscope, a little starch, with a sufficient quantity of water, 

 is to be put, and the former well spread out with the finger, to prevent, as much as 

 possible, the formation of bubbles, The number of starch grains in the field of view 

 should not exceed ten or fifteen. The glasses should He freely on the spring-piece, 

 which must be raised by means of two pieces of cork, introduced below it, so that 

 while the two glasses are lying right upon the object-bearer, a current of cold air will 

 ascend from below, and permit the little flame to continue burning in the hole of or 

 below the stage. As the glasses are wide they protect the microscope from too great 

 a heat or other danger. The small flame is to be obtained from a common thread, 

 doubled and slightly waxed. This, when ignited, gives a flame quite sufficient to boil 

 the starch." The object of this experiment is to cauee the distension of the cell-wall 

 by the introduction within the cell of hot water, and thereby to notice what changes 

 take place in the markings upon the surface. 



Mr. Busk seeks the same end by applying the most powerful of acids m., concen- 



