758 SUMMARY OF CURRENT RESEARCHES RELATING TO 



exist togotlaer in the stavch-granule, the granule can be turned yellow 

 by iodine after the grauulose has been extracted. 



The reactions of starch are so delicate that they can be recognized 

 in the very small starch-granules contained in the chlorophyll- 

 bodies. The colouring by iodine is distinctly visible when care is 

 taken to render the chlorophyll-body transparent by acetic acid, 

 or to increase its permeability by submitting it to the action of 

 potash. 



In the Euglence there is a variety of starch called paramylon, 

 formed of long cylindrical rods, disks, or ellipsoid bodies; when 

 coloured yellow by iodine it appears exactly similar to amylose. 



Certes,* by making use of the iodized serum described by Eanvier,| 

 has demonstrated in several Infusoria an amylaceous substanco 

 coloured mahogany-brown or wine-red by this reagent. He considers 

 it as identical with the glycogenous matter, the existence of which 

 was shown by C. Bernard in the liver of the higher animals and of 

 many Invertebrates. It is probable that it exists with these same 

 characters in many plants, the percentage constitution of starch and 

 of the substance called glycogen being the same. 



Tannins. — Salts of iron are the reagents for the tannic acids. They 

 generally colour them black or dark blue, sometimes green. Acetate 

 of iron gives a very deep blue colour, and chloride of iron a dark 

 green ; chromate of potash, alcoholic solution of auilin-violet and 

 dilute chloriodide of zinc may also be used. The tannins become 

 brownish red in the first case, red in the second, red or violet in the 

 third. 



The development of Penicillium glaucum and of Sterigmatocystts 

 nigra in a solution of tannin exposed to the air separates the tannin 

 into glucose and gallic acid. Perhaps this phenomenon is due to a 

 diastase formed in very small quantities in the cells of the plant. 

 The same division takes place with dilute acids. It is probable that 

 it also takes place in the interior of tanniferous cells by the progress 

 of vegetation, for these cells are sometimes seen gradually to lose 

 theii' tannin, in proportion as they acquire more and more glucose, 

 a transformation which is particularly evident during the ripening 

 of fruits. I This is an interesting subject of study ; we can by 

 micro-chemistry exactly determine the localization of the tannin ; it 

 would be very important to follow its metamorphoses. The difficulty 

 probably lies in distinctly showing the diastase, for there are many 

 ways by which the sugars may be revealed. 



Sugars. — Sulphate of copper, followed by the action of potash 

 after washing, gives a colour to the sugars which enables them to 

 be recognized in the tissues of plants. But the colouring differs 

 according to whether the sugar belongs to the group of saccharoses 

 (Ci2H220n) or glucoses (C,;Hi^O,;). Poulsen § recommends the follow- 

 ing process : Make a tolerably thin section of the tissue ; immerse it 



* Comptes Eendus, 12th January, 1880. 



t ' Traite teclinique d'Histologie,' p. 158, 



X Van Tieghem, ' Triiite de Botauique,' 1SS2, p. 512. 



§ Log. cit., p 33, 



