50 THE VEGETABLE CELL IN GENERAL. 



formation of starch-paste, and bring about some other changes, 

 such as its conversion into soluble matters. 



179. Starch is usually said to have the following composition, 

 C 6 H 10 O-, and these proportions are doubtless correctly stated ; 

 but it is probable that the molecular constitution is more com- 

 plex than this formula would indicate. 1 



180. When starch is acted on b}' saliva or pepsin, it is slowly 

 separated into two substances, one of which passes into solution, 

 while the other remains as a skeleton, and with little change of 

 form. This delicate framework, which remains after the soluble 

 matter is removed, is closely related to cellulose, as shown by 

 its behavior with reagents, and has received the name of starch 

 cellulose. The substance which is removed b} T the action of saliva 

 is termed gramdose. 



181. When starch is not associated with too large a propor- 

 tion of protein matters, it can always be detected by the blue 

 color which it takes with iodine in solution ; but if protein sub- 

 stances are present in considerable amount, they may obscure 

 the reaction by the yellowish or brown color which iodine im- 

 parts to them. Iodine does not, however, always produce a blue 

 color with starch ; the shade may vary towards red, forming a 

 purple which may be almost black. Furthermore, as the tran- 

 sient color given by this reagent fades, it may pass through 

 various tints of orange and vellow. 



o / 



Protein matters which mask the starch reaction ma} T be re- 

 moved by careful treatment of the specimen with potassic hy- 

 drate (not too concentrated), and subsequent washing with pure 

 water. After such treatment it sometimes happens that the 

 starch appears as a diffused mass instead of in minute dots. 



182. When starch-granules are seen in polarized light they 

 generally exhibit two crossed lines which appear to turn as the 

 Nicol prism is revolved. Man}' kinds of starch give under the 

 polarizer characteristic figures, many of them of great beauty. 



183. I n ii I in. although occurring in solution in cells, is never- 

 theless thrown down in characteristic forms by means of the 

 preservative media alcohol and glycerin, and can be examined as 

 a solid. If the root of Dahlia, Helianthus, or any of the com- 

 mon Composite which store up their food in flesh}' underground 

 parts, be subjected to the action of alcohol for a few days, thin 

 sections will exhibit in the cells peculiar masses of a spheroidal 



1 "W. Nageli, however, gives the formula for starch as follows : 

 Beitr. z. naheren Keimtniss der Starkegruppe, 1874. 



