A Popular History of British Lichens (Paperback)

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER II. GENERAL CHARACTERS OF BRITISH LICHENS. " Some are reddish, some brown, some grey, aud some black, Aud they're puckered, edged, button'd, or fringed, front and back: Some are lying like leather close under your feet, Some waving from trees in the forest you '11 meet."?Miss Twamley. We shall here consider the minute or microseopic anatomy, as well as the ordinary physical aud chemical characters of the vegetative and reproductive systems of Lichens, and shall also review generally the biology of a Lichen, tracing the various phases of its existence from its origin to its decay. The term Thallus ( aXXo?, a frond or green leaf, ) is generally employed to designate the vegetative system or mass of nutritive organs of a Lichen. Though bearing no structural resemblance to either, it may be considered as combining the offices and supplying the place among the Lichens of the stem, root, and leaves of the higher plants. In formit is typically horizontal or vertical, according to the intimacy of its adhesion to its base of support, and the direction and mode of development of its constituent cells. The subdivisions or modifications of the horizontal, or typically adherent, thallus, are the crustaceous and the folia- ceous, or frondose. The crustaceous thallus forms a mere crust or coating, of varying thickness, on its base of support. When comparatively thick, dense, and hard, it is denominated tartareous, as in many Lecanoras; this form is frequently whitish or pale-coloured, chalk-like, friable, and rough or warted on its surface. As constituent elements, it often contains a considerable amount of mineral matter, such as the carbonate and oxalate of lime, besides colorific principles capable of yielding valuable purple pigments; hence many Lichens having this form...