LICHENS.

Auckland Star, Volume LIII, Issue 78, 1 April 1922, Page 22

LICHENS.

THEIR NATURE AND USES. NATURE'S PIONEERS. The lowly forms of vegetation known as lichens attract very little attention from the ordinary observer. Even the famous Swedish botanist Linnaeus scorned them as "the poor trash of vegetation," although he named and listed 80 species. To-day more than 4000 different species have been classified, and a careful study of their characteristics and the conditions under which they grow has thrown a good deal of light upon the uses of these humble plants in Nature's laboratory. A great deal of this information is embodied in a very interesting book by Annie Lorrain Smith, F.Z.S., acting-assistant, Botanical Department of the British Museum, which has been published by the Cambridge University Press. These humble plants seem to have played an Important part in the vegetable world. "They are most of them undoubtedly very old plants, and were probably widespread before continents and climates had attained their present stability." A large part of the presentday lichens are believed to have -een evolved at the end of the Tertiary period.

The author states that lichens are, with few exceptions, perennial aerial plants of somewhat lowly organisation. In the form of spreading encrustations, horizontal leafy expansions of upright strap-shaped fronds, or of pendulous filaments, they take possession of the tree-trunks, palings, walls, rocks, or even soil that afford them a suitable and stable foothold. They abound everywhere, from the seashore to the tops of high mountains, where, indeed, the covering of perpetual snow is the only barrier to their advance; but, owing to their slow growth and long duration, they are more seriously affected than are the higher plants by chemical or other atmospheric impurities, and they are killed out by the smoke of large towns. The climatic factors most favourable to lichens are direct light, a moderate or cold temperature, constant moisture, and a clear pure atmosphere. Lichens can also endure the heat of direct sunlight. They play an important part in dissolving rocky surfaces and preparing soil for other plants. Observation has shewn that even such hard substances as chalcedony and granite are corroded by a very luxuriant lichen flora. The corrosive action is due to the carbon dioxide given off by the plant, though oxalic acid, so frequent a constituent of lichens, may a'so share in the corrosion. They change quartz into amorphous silicic acid, and thus bring it into the cycle of organic life.

The Antarctic flora prevails more or less in the extreme southern part of America, and the similarity between the lichens of that country and those of Xew Zealand is very striking. There is a very abundant flora in New Zealand, with its «001, moist climate and high mountains.

The author of this notable addition to the Cambridge Botanical Handbooks has dealt with the subject in a most exhaustive manner, historically and botanioally. It may be readily believed that she has left little unsaid that is worth saying in this division of botanical knowledge, and her classifications of thousands of species are arranged in a form that will facilitate research by anyone whose attention is attracted to this branch of 6tudy.