102 BOTANICAL MICROTECHNIQUE. 



matters called chlorophyll-yellow, xanthophyll, erythrophyll, 

 chrysophyll, etc. According to Immendorff (I, 516), carotin 

 also occurs in the chromatophores of etiolated parts of 

 plants and is the cause of the autumnal yellowing of leaves. 



171. The elementary composition of carotin corresponds 

 to the formula C 26 H 38 , according to Arnaud (I) ; it would 

 therefore clearly constitute an hydrocarbon. According to 

 Immendorff (I, 510), it is precipitated in shining, deep-red 

 crystals by alcohol, from its solution in carbon bisulphide, 

 which it colors deep blood-red. These crystals show, when 

 undecomposed, a strong dichroism (cf. 356, note) ; but on 

 lying in the air they take up oxygen and pass over gradually 

 into a colorless compound readily soluble in alcohol. On 

 ^warming they first take a brick-red color, and above 160 C. 

 they melt. 



Courchet has prepared very variously shaped crystals of 

 carotin from various parts of plants which showed, like 

 those observed naturally, sometimes a red, sometimes a 

 more yellow color. It is still unknown to what these differ- 

 ences in color, which are to be seen in one and the same 

 cell in the carrot, are to be referred. It is also yet to be 

 determined whether all the coloring matters called carotin 

 .are identical ; for it seems probable that we have to do here 

 at least with a group of nearly related coloring matters. 



172. The following reactions may serve for the micro- 

 chemical recognition of carotin : With a solution of iodine 

 {e.g., aqueous solution of iodine and iodide of potassium), it 

 is colored greenish or greenish blue ; with concentrated sul- 

 phuric acid, first viokt and then indigo-blue ; from its deep 

 blue solution in concentrated sulphuric acid it is precipitated 

 in green non-crystalline flakes, on the addition of water, ac- 

 cording to Immendorff (I, 509). 



Carotin is also, according to Arnaud (I), insoluble in 

 water, almost so in alcohol, very slightly soluble in ether, 

 more readily so in benzine, and most so in chloroform and 

 carbon bisulphide. 



These solutions, even when from carmine-red crystals, are 

 colored yellow or orange-yellow, according to their concen- 



