760 SUMMABY OF CURRENT RESEARCHES RELATING TO 



stances is the alcobolic tincture of alkanet. The colouring matter is 

 extracted from the roots of Alkanna tinctoria. The tincture colours 

 red, not the individual drops of oil, but the entire mass composed of 

 these drops and the protoplasm which contains them, when they are 

 in sufficiently large quantity. This is also the case with oleaginous 

 seeds. The reagent shows that the oil is always outside the grains 

 of aleurone.* 



Tincture of alkanet also colours the resins red. 



Cyanin is also used as a reagent for oily matters. These sub- 

 stances absorb very energetically the colouring matter of the aqueous 

 or alcoholic solution of quinolein blue. The smallest oily particles 

 of the protoplasm thus acquire a great distinctness, as has been shown 

 by the experiments of Certes f on many lower organisms, animal and 

 vegetable. 



Gums. — The anilin colours stain deeply the mucilaginous mem- 

 branes which iodine alone or iodine used after the action of sul- 

 phuric acid does not colour blue. Chloriodide of zinc gives them a 

 yellow colour ; they assume, according to SollaJ and Hohnel,§ a fine 

 yellow colour after being immersed for some time in ammonia, to 

 which nitrate of potash has been added. 



Cellulose. — The cellulose of the cell-wall has the formula Cg Hjo O5 ; 

 it exists in plants in different stages of condensation. 



The polymere (C^ Hio Os)^, which may be taken as the type of 

 cellulose, is not turned blue by iodine, but shows a fine blue colour 

 after treatment with iodine and sulphuric acid. The polymere 

 (Ci; Hi!) 0.5)3, which is rather rare, turns blue directly with iodine 

 like granulose. The same takes place with the paraphyses and the 

 walls of the asci of the lichens and of many fungi. 



Good results have been obtained with an iodized solution of the 

 strength of 1 gr. of iodine in 3 gr. of iodide of potassium and 600 gr. 

 of water. 1 1 



Sulphuric acid and iodine are used in succession. The iodine 

 may be in an aqueous or alcoholic solution. The sulphuric acid may 

 be replaced by phosphoric acid. Instead of using the two agents, iodine 

 and sulphuric acid successively, a single reagent may be substituted 

 which has the same effect, chloriodide of zinc. It is very important 

 to observe that the chloriodide of zinc cannot be rigorously defined 

 quantitatively ; the same reagents not suiting all species of plants 

 equally well. The chloriodide of zinc which may have just given 

 excellent indications on sections of one species, does not act effectively 

 on another species. This is because the vegetable cells contain 

 different substances, which, in many cases may prevent the reaction. 



* Poulsen, loc. cit., p. 41. 



f Cf. Balbiani, ' Keclierches sur les phenomeues sexiiels des lafusoires,' note 1, 

 p. 27, 18G1. Ranvier, loc. cit, p. 102. Cerfes, " Sur un precede de coloration dea 

 Infusoires," Comptes Rendus, 8tfi March, 1881. 



X " Mittellamelle des Holzelemente u. d. Hoftiipfel Schliessmembran," Bot. 

 Ztg., 1880, No. 26. 



§ See Poulsen, loc. cit. p. Gl. 



II "Beitr. zur Kenutniss d. chem. und phys. Beschaffenheit der Intercellular- 

 substanz," Oester. Bot. Zeitsclir., 1879. 



