370 STRUCTURE OF PHANEROGAMIC PLANTS. 



capillary attraction, instead of running down and leaving the 

 object, as it will do if the glasses be too widely separated. 



229. In some part or other of most Plants, we meet with cells 

 containing granules of Starch. These granules are sometimes 

 minute and very numerous, and are so closely packed together 

 as to fill the cavity (Fig. 159) ; in other instances they are of 



Fig. 159. Fig. 160. 



Cells of PtEoray, filled with Starch. Granules of Starch, as seen under polarized 



light. 



much larger dimensions, so that only a small number of them 

 can be included in any one cell ; while in other cases, again, 

 they are both few and minute, so that they form but a small 

 proportion of the cell-contents. Their nature is at once detected 

 by the addition of a solution of iodine, which gives them a 

 beautiful blue color. Each granule exhibits a peculiar spot termed 

 the Mlum, which marks the point at which, in its early state, it 

 is attached to 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 po- 

 larized light (§ 63), each grain exhibits a beautiful dark cross, 

 the point of intersection being at the hilum (Fig. 160). Eegard- 

 ing the internal structure of the starch grain, opinions are very 

 much divided ; for whilst some affirm the concentric lines to 

 indicate the existence of a number of concentric lamellse, one 

 enclosing another, others consider that they are due to the 

 peculiar plaiting or involution of a single vesicular wall;^ and 

 among those who consider it to be concentrically lamellated, 

 some hold that each lamella is formed outside or upon that which 

 preceded it, while others consider that each is formed inside or 

 within its predecessor. The centre of the granule is often occu- 

 pied by starchy matter in an unconsolidated state ; and it is the 

 appearance arising from its difterent refractive power, that has 

 caused some observers to describe the starch-grain as possessing 



' The first of these opinions is the one which had been generally received until 

 recently, when Mr. G, Busk supported the latter by new observations made upon the 

 unfolding of the starch-granule by dilute sulphuric acid; since when, Prof. Allnian, 

 after repeating Mr. Busk's observations, 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 Miorosc. Soe." ser. 2, vol. i, p. 58 ; and that of Prof Allman in " Quart. 

 Journ. of Miorosc. Sci." vol, ii, p. 163. 



