CELL-CONTENTS. — STARCH. 



341 



cause of its errhine properties when powdered and used as 

 snuff. It is in the underlying or true epidermis, that the 

 silica occurs. This membrane is permeable by fluids, not 

 by means of pores, but by endosmotic force. 



The most generally-distributed and conspicuous of the 

 cell-contents is Starch; at BWi^yg^c^-y^ySfg 

 the same time it is one of W^^fM0^^M^A^fi\ 

 great value and interest, per- 

 forming a similar office in 

 the economy of plants as that 

 of fat in animals. It occurs 



in all plants at some period of 

 their existence, and is the 

 chief and great mark of dis- 

 tinction between the vege- 

 table and animal kingdoms. 



Its presence is detected by P^J^f^'^Q&t 

 testing with a solution of fe^^^^^^®| 

 iodine, which changes it to W$&% ; j[f$^fM^t : i 

 a characteristic blue or violet 

 colour. 1 Being insoluble in 



COld Water, it Can be readily Tig.lSl.— Section of a Cane; with cell- 

 ij j ,i tcalls of silica, and internal pores 



washed away and separated fillet with granular matter. 

 from other matters contained 



in the cellular parts of full-grown plants. It is often 

 found in small granular masses in the interior of cells, 

 shown in fig. 183 from the garden-rhubarb. Starch-grains 

 are variable in size; the tous-les-mois, fig. 188, No. 5, are 

 very large ; in the potato, No. 14, they are smaller ; and 

 in rice, No. 6, they are veiy small indeed. Nearly all pre- 

 sent the appearance of concentric irregular circles ; and most 

 of the granules have a circular spot, termed the hilum, 

 around which a large number of curved lines arrange them- 

 selves : better seen under polarised light. Plate VIII. No. 167. 

 Leeuwenhoek, to whom we are indebted for the earliest 

 notice of starch-granules, enters with considerable minute- 

 ness into a description of those of several plants — such as 

 wheat, barley, rye, oats, peas, beans, kidney-beans, buck- 

 wheat, maize, and rice ; and very carefully describes 

 experiments made by him in order to investigate the 

 structure of starch- granules. Dr. Heissek regards the 



(1) This is not a test for starch when combined with albuminous matters. 



