48 The Irish Naturalist. April, 1922. 



NOTES. 



BOTANY. 



Lichens on Veronica Traversii. 



Two large shrubs of Veronica Traversii in the garden of Lehenagh 

 House, Cork, were found in 19 18 to be so infested with lichens that the 

 larger branches were weighed down dangerously and the shrubs were in 

 a thoroughly unhealthy state. Both measured about 12 feet in diameter. 

 One, which was the more shaded, was almost completely broken down. 

 Its outer branches, having been propped up with sticks and tied together 

 with string, made a canopy inside which new shoots were struggling to 

 form a healthy shrub. The other had retained its conical form but the 

 leaves were limited to the extreme tips of the branches, the inside of the 

 hut thus form^ed being grey with an extraordinarily luxuriant growth of 

 lichens. The neighbouring rhododendrons, laurels and barberries showed 

 little trace of lichen growth. An examination was therefore made to 

 find out the reason for this selection and the best way to save the shrubs. 

 The reason was found to lie in the peculiar character of the bark of this 

 species of Veronica. A young healthy twig has an indentation in the 

 bark at the base of each pair of the decussate leaves. In slightly older 

 twigs this becomes a distinct furrow, encircling the twig by the time the 

 leaf falls. In the furrow water, algae, fungal spores and other debris collect 

 and form an ideal nest for lichens. In an unhealthy state the leaves would 

 fall off early, leaving the bark softer, and therefore more easily penetrable 

 by lichen rhizoids. A well-established lichen may cast off its spores or 

 soredia to be washed or blown into a suitable crevice. There, if conditions 

 are favourable, a new lichen slowly develops. But also, if a lobe of the 

 old lichen chances to touch a suitable spot on the bark, it may, like a 

 gooseberry sucker, give rise to a new plant. The distance between the 

 furrows of this Veronica are well fitted for this mode of reproduction, so 

 that the upper surface of an old branch is easily covered by a matted 

 tangle of shrubby lichens. Inside the twig the bark is broken by the 

 wedge-like action of the rhizoids. In this furrows this disintegration is 

 the more serious because the living tissues of the bast are nearer the 

 surface and are touched though not directly attacked by the fungal 

 threads. The bark is thus loosened into a series of rings, a process which 

 normally takes place so gradually that the stem has time to develop a 

 new bark in place of the old. 



The rotten branches of one shrub were cut away, and the new growth 

 is as yet free from lichens. The other has been pruned so as to allow 

 more light and air to enter. It is now in a healthier state. The following 

 species of lichens were identified -.^Ramalina farinacea, R. Jastigiata, 

 Evernia prunastri ; Usna hirta ; Parmelia sulcata, perlata, physodes, 

 caper ata, exasperata ; Lecanora sulpisca ; Gr aphis scupta ; Graphina 

 anguina* 



Cork. Lilian Porter. 



