DR LAUDER LINDSAY ON NEW LICHENICOLOUS MICRO-FUNGI. 523 



in the first place, that we should possess some trustworthy information as to the 

 chemistry of the reaction, and as to the nature of those substances which, in 

 lichens and fungi respectively, yield colour-reactions with iodine. As regards 

 the lichens, I have carefully studied the most recent and approved standard works 

 in chemistry; and the result is, that I find a discrepancy and confusion of asser- 

 tion and opinion among chemists, nearly as great as that which exists between 

 lichenologists and fungologists in regard to the application of the test, or of its 

 colour-reaction, as a botanical " character." 



So far as I have been able to ascertain, the substances occurring in lichens, 

 which give colour-reactions with iodine, of the class which is now under review, 

 are the following : — 



I. Starch or its modifications. 



A. Lichenine, Syn. Lichen starch, Lichenic acid. Formulas, C 6 H 10 O 5 , C 12 H 10 O 10 

 (Gregory).* Has been examined by chemists as it occurs in Cetraria Islandica 

 and aculeata, Sticta pulmonaria, Ramalina fraxinea, Usnea barbata, Physcia 

 parietina. 



Chemical characters. — Isomeric with starch. In C Islandica does not occur 

 in granules ; but is uniformly distributed through the tissues in a soluble con- 

 dition. Pure lichenine is merely coloured yellow by iodine ; but a green or blue 

 is often produced from admixture of starch (Watt).| A colourles jelly " some- 

 times assumes a blue, and sometimes a greenish tint," with iodine (Gorup 

 Besanez).| Gives with iodine a greenish-brown colour (Kane).§ "Its solu- 

 tion is not coloured by iodine ; but the jelly is rendered blue by that test" 

 (Gregory). Other authors describe the reaction with iodine as blue, and this is 

 the reaction (generally) assumed by lichenologists as the basis of theiiiodine- 

 testings. 



B. Inidine, Syn. Dahline, Alantine, Menyanthine, Datiscine|| (Gregory). 

 Formidae, C 12 H 10 O 10 (Gregory), C 24 H 2l 21 (Parnell). Has been examined as it 

 occurs in Cetraria Islandica in association with lichenine. 



Chemical Characters. — Also isomeric with starch. Occurs in white, crystal- 

 line grains. Sparingly soluble in cold, very soluble in hot, water. Iodine colours 

 it slightly brown (Gregory). Insoluble in alcohol. Not blue, but yellow, with 

 iodine (Miller). 



C. Starch. Formula, C 12 H 10 O 10 . Has been examined as it occurs in Rama- 

 lina fastigiata (in large quantity); and Cladonia macilenta, digitata, and uncialis 

 (Watt). It does not quite clearly appear whether this is ordinary starch in its 



* " Handbook of Organic Chemistry," 4th edition (1856;. 

 t "Dictionary of Chemistry," 5 vols. (1860-68). 

 X Quoted in " Chambers's Encyclopaedia," 10 vols. (1860-68). 

 § " Elements of Chemistry," 2d. ed. (1849). 



|| Miller ("Elements of Chemistry," 2d ed., 1862, p. 597") gives Datiscine ( = C 42 H 22 24 ). 

 as the colorific principle of Datisca cannabina — not as a starch ! 



