Nov. 1, 1S67.] 



HARDWICKE'S SCIENCE-GOSSIP. 



211 



IS LICHEN-GROWTH DETRIMENTAL TO TREES? 



By DR. LAUDER LINDSAY, F.L.S.* 



HERE is, it would 

 appear, a radical 

 difference of opinion 

 between lichenolo- 

 gists on the one 

 hand, and arboricul- 

 turists on the other, 

 as to the effect on 

 the value of the tim- 

 ber and bark of the 

 which it occurs, of 

 Lichen-growth. Lichenologists 

 have been in the habit of de- 

 scribing Lichens as deriving 

 their nourishment wholly from 

 the air — as non-parasitic — and 

 as making use of trees simply 

 as bases of support.^ Some, es- 

 pecially of the earlier writers, 

 not only deny any possible 

 harm, but demonstrate a con- 

 siderable amount of actual 

 good, in so far as Lichens at- 

 tract moisture to the trees on 

 which they occur, and thus assist in theirnourishment 

 and growth. J All " practical men," on the other 

 hand, all those who are concerned with the cultivation 

 of timber, bark, or fruit trees, without theorising on 

 the subject, are unanimous in describing Lichens as 

 detrimental to growth, and as depreciative of value. 

 My friend Mr. Anderson, of the Kinnoull Nurseries, 

 Perth, tells me that trees or shrubs coated with 



* The substance of a paper read before Section D of the 

 British Association at Dundee. 



+ Nylander, in his " Synopsis " (Introduction, p. 1), says that 

 the majority are exclusively nourished by the atmosphere. 



Berkeley in the " Treasury of Botany " (p. 6;a), says Lichens 

 are " distinguished from Fungi by their not deriving nourish- 

 ment in general from the substances on which they grow, but 

 from the surrounding medium." 



% Vide " Tentamen Historise Lichenum." By J. A. Luyken, 

 M.D. GSttingen, 1S09, p. 32 and seq. 



No. 35. 



Lichens, are " immediately discarded as unsaleable ,-" 

 while Mr. Bell, factor on the Kinfauns estates, gives 

 me a similar assurance as to the diminished value of 

 oak-bark when infested by Lichens.* Mr. Gorrie, 

 Horticultural Editor of the Farmer, and one of the 

 most experienced and discriminating arboriculturists 

 in Scotland, Mr. Moore, of the Sydney Botanic 

 Garden, . New South Wales, and other practical 

 authorities, whose opinions carry great weight in 

 such a question, have borne similar testimony. My 

 inference from their testimony is that they regard 

 Lichens as true parasites, living, in great measure 

 at least, at the expense of the bark on which they 

 occur; interfering with its healthy action and 

 growth. While regarding Lichen-growth, however, 

 as in a certain sense, or in some measure, a cause of 

 unhealthiness or disease in the trees which it affects, 

 they also admit that, in a certain other sense, it is a 

 result of unhealthiness or disease. The evidence 

 appears uniform that Lichen-growth should never 

 occur in forests or nurseries, which are the subject 

 of proper care, where the trees or shrubs are properly 

 thinned,t where the conditions of healthy growth 

 are sedulously provided. Not only so, but I am 

 assured that the disease of Lichen-growth, when it 

 occurs, can be removed or dissipated by removal of 



* He writes to me (March, I807), " It is much against the 

 growth of the trees as well as the bark. You wiU scarcely 

 find it in a good thriving plantation." 



f My own observations are here somewhat at variance 

 with the statements of Arboriculturists. In the Kinfauns 

 Plantations I find some trees bare : others copiously covered : 

 but the latter are as frequently in vigorous life, with a 

 plentiful foliage, as dead. It is impossible in such instances to 

 infer that Lichens are necessarily either a cause or result of 

 disease. Moreover, all my experience in different parts of the 

 world goes to prove that Lichen-growth is most abundant 

 and vigorous in those situations, which are most freely exposed 

 to light and air : of which familiar illustrations are to be found 

 in maritime rocks and Druidical stones, that are frequently 

 "shaggy" with a plentiful mantle of Ramalina scopulorum 

 and other Lichens. 



M 



