CHAPTER X 



ECONOMIC AND TECHNICAL 

 A. LICHENS AS FOOD. 



a. FOOD FOR INSECTS, ETC. Some of the earlier botanists made careful 

 observations on the important place occupied by lichens in nature as affording 

 food to many small animals. In 1791 Jacques Brez 1 wrote his Flore des 

 Insectophyles, and in the list of food-plants he includes seven species of 

 lichens. The "insects" that frequented these lichens were species of the 

 genera Acarus (mites) and Phalena (moths). A few years later Persoon 2 

 noted that lichens formed the main food supply of many insects, slugs, etc. 

 Zukal 3 , quoting from Otto Wilde (Die Pflanzen und Raupen Deutschlands, 

 Berlin, 1860), gives a list of caterpillars that are known to feed on and 

 destroy lichens. 



A very considerable number of small creatures feed eagerly on lichens, 

 and traces of their depredations are constantly to be seen in the empty 

 fruit discs, and in the cortices eaten away in patches so as to expose the 

 white medulla. It has been argued by Zukal 4 that the great formation of 

 acid substances in lichens is for shielding them against the attacks of 

 animals; Zopf 5 on the contrary insists that these substances afford the plants 

 no real protection. He made a series of experiments with snails, feeding 

 them with slices of potato smeared with pure lichen acids. Many snails ate 

 the slices with great readiness even when covered with bitter acids such as 

 cetraric, or with those which are poisonous for other animals such as rhizo- 

 carpic and pinastrinic. The only acid they refused was vulpinic, which is 

 said to be poisonous for vertebrates. The crystals of the acids passed 

 unchanged through the alimentary canal of the snails, and were found in 

 masses in the excreta. They were undissolved, but, enclosed in slime, their 

 sharp edges did no damage to the digestive tract. 



Stahl 6 however upholds Zukal's theory of the protective function of 

 lichen acids against the attacks of small animals. Some few snails, cater- 

 pillars, etc., that are omnivorous feeders consume most lichens with impunity, 

 and the bitter taste seems to attract rather than repel them ; but many 

 others he contends are certainly prevented from eating lichens by the 

 presence of the acids. He proved this by soaking portions of the thalli of 

 certain bitter species for about twenty-four hours in a one per cent, soda 

 solution, which was sufficiently strong to extract the acids. He found that 



1 Brez 1791. 2 Persoon 1794. 3 Zukal 1895, p. 1317 (note). 4 Zukal 1895, p. 1315. 

 6 Zopf 1896. Stahl 1904. 



