STARCH-GRANULES. 399 



the cell-wall ; and it also presents, when highly magnified, a set of 

 circular lines, which are for the most part concentric (or nearly so) 

 with the Hilum. When viewed by Polarized light, each grain 

 exhibits a dark cross, the point of intersection being at the Hilum 

 (Fig. 209) ; and when a Selenite-plate is interposed, the cross 

 becomes beautifully coloured. Opinions are very much divided 

 regarding the internal 



structure of the Starch- fro. 2oq. 



grain ; for whilst some 

 affirm the concentric lines 

 to indicate the existence 

 of a number of concentric 

 lamella?, one enclosing 

 another, others consider 

 that they are due to the 

 peculiar plaiting or in- 

 volution of a single vesi- 

 cular wall ; * and among 

 those who consider it to 

 be concentrically lamel- Granules of Starch, as seen under 

 lated, some hold that each Polanzed U ^ 



lamella is formed outside 



or upon that which preceded it, while others consider that each 

 is formed inside or loithin its predecessor. The centre of the 

 granule is often occupied by starchy matter in an unconsolidated 

 state; and the appearance arising from the different refractive 

 power of this has caused some observers to describe the Starch 

 grain as possessing a Nucleus. — Although the dimensions of the 

 Starch-grains produced by any one species of Plant are by no means 

 constant, yet there is a certain average for each, from which none 

 of them depart very widely ; and by reference to this average the 

 Starch-grains of different plants that yield this product in abun- 

 dance may be microscopically distinguished from one another, a 

 circumstance of considerable importance in commerce. The largest 

 Starch-grains in common use are those of the plant (a species of 

 Canna) known as Tons les mois ; the average diameter of those 

 of the Potato is about the same as the diameter of the smallest of 



* The first of these opinions is the one which was generally re- 

 ceived, until Mr. G. Busk supported the latter by new observations 

 made upon the unfolding of the starch-granules by dilute sulphuric 

 acid ; since when, Prof . Allman, after repeating Mr. Busk's observa- 

 tions, has been led to affirm them to be fallacious, and to revert to 

 the first of the above-mentioned doctrines. — See Mr. Busk's memoir 

 in " Trans, of Microsc. Soc." 2nd Ser. Vol. i. (1853), p. 58, and that of 

 Prof. Allman in " Quart. Joum. of Microsc. Science," Vol. ii. (1854), 

 p. 163 ; also Cruger, on the Development of Starch, in the same volume, 

 p. 173 ; Grundy in " Pharmaceutical Journal," April, 1855 ; Henfrey in 

 Ann. of "Nat. Hist." Ser. 2, Vol. xv. p. 246; and Eainey in "Quart. 

 Joum. of Microsc. Science," Vol. viii. (1860), p. 1. 



