LICHENS 



The primary object of this chapter is not to describe the species 

 of Hcliens met with in this country. There are two reasons for 

 this statement : (i) My inabihty to do so ; (2) as there are, in 

 round numbers, 2000 British species, the requisite space is not 

 forthcoming in a single volume. What should be done, and what 

 I hope may be done, is the production of a volume devoted solely 

 to the study of this beautiful and highly interesting group of plants. 



During mycological rambles the student is certain to meet with 

 many of the commoner species of lichens, which in many instances, 

 superficially, so closely resemble certain groups of fungi, both in 

 habit and general appearance, that a few hints on the principal 

 points of distinction between fungi and lichens may be acceptable. 

 In the second place, some of the larger, frondose lichens, that can- 

 not be mistaken for fungi, are fairly abundant and are certain to 

 attract attention, and it is just as well that the names and afhni- 

 ties of such forms should be known. With this object in view, two 

 plates of figures of lichens are given, mainly for the puri)ose of 

 enabling the student to gain some idea of the general appearance 

 of the various types of plants collectively constituting the Order 

 Lichenes, and not with the idea of indicating definite species. 



One very pronounced difference between fungi and lichens 

 turns on the nature of the food. In fungi, it will be remembered, 

 organic food is required ; whereas in lichens inorganic food — that is, 

 carbonic dioxide obtained from the air, and certain salts and other 

 substances in solution in water — are required. The above is the 

 distinction between lichens and fungi, so far as food is concerned, 

 as usually given in text-books, and, broadly speaking, it is correct ; 

 but if we investigate the matter in detail, we find that there are 

 exceptions to the rule. Some lichens are injurious parasites on 

 living leaves and branches, and the mycelium of certain fungi often 

 appear and grow vigorously in dilute solutions of mineral acids or 

 salts. Owing to the nature of their food, fungi are never pioneers, 

 or the first signs of life to appear in a previously sterile region ; 

 whereas lichens, whose food is supplied by the air and the soluble 

 portions of disintegrated rock, are amongst the first living organisms 

 to appear in those inhospitable regions where no other form of life 

 could exist. This is rendered possible by the pecuhar constitution 



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