STARCHES. 145 



particles are smaller, and the markings observed in the granule, 

 together with the hilum or nucleus, are caused by the greater or 

 less amounts of water, and therefore alteration of refractive power 

 in various parts of the granule. The stratification of a starch- 

 grain disappears when the water is wholly removed either by 

 drying or by chemical re-agents, or when it is rendered equally 

 aqueous in all its parts. This abstraction of water may be accom- 

 plished by the action of absolute alcohol, whilst the absorption of 

 water may be effected by treatment with dilute solution of potash. 



Starch-granules, although rendered blue in all their parts by 

 iodine, yet consist of two distinct modifications — granulose, which 

 is the more soluble and readily acted on by iodine, and starch 

 cellulose, which is not so readily acted on. This latter is present 

 only in the proportion of from two to six per cent. Granulose may 

 be extracted either by saliva or by a saturated solution of salt, 

 containing one per cent, of hydrochloric acid. 



It is not absolutely known what are the principles in the plant 

 from which starch is precipitated, but here an observation of 

 Rainey's offers a valuable suggestion. He found that a mixture of 

 gum and dextrine, whether in acid or alkaline solutions, caused a 

 precipitation of true starch particles. The best way to observe it 

 under the microscope is to acidify a solution of dextrine with citric 

 acid, and under the microscope to treat first with gum and then 

 with iodine, or the iodine may be added first and the gum after; 

 in either case, colourless starch corpuscles are first formed, turning 

 blue as they unite with the iodine. Now, as we know that gum, 

 dextrine, or their isomers are always present in living plants, it is 

 but reasonable to suppose — although the fact has not been actually 

 demonstrated — that these substances play an important part in 

 starch formation ; we should thus find in the plant a gradual 

 transformation of starch into dextrine, sugar, and gum, etc. ; and 

 again the re-formation of these bodies into starch to act as a 

 reserve food in the process of further cell formation. 



With respect to this portion of our subject, it is found that 

 starch is not usually produced in the living plant except in pre- 

 sence of chlorophyll. In a perfectly dark place, where green 

 chlorophyll cannot be formed, there starch is not usually produced, 

 and if starch, which has been formed under the action of chloro- 



International Journal of Microscopy and Natural Science. 



New Series. Vol. III. l 



