BIONOMIC CHARACTERS OF PLANTS 1003 



ing either parasites (growing upon living organisms) or saprophy- 

 tes (growing upon dead organic matter) or both parasitic and 

 saprophytic. Fungi can thus grow in the dark regions of the 

 earth, sunHght not being essential. They are mostly terrestrial 

 (when not living within their host), though some marine repre- 

 sentatives are known, and certain of the molds (phycomycetes) 

 form on decaying animals in fresh water or sometimes on living 

 fish or Crustacea. The large terrestrial fungi are most characteristic 

 of the temperate zones, the tropical species being mostly small. 



Lichens. Lichens are terrestrial plants growing chiefly upon 

 the bark of trees, rocks, the ground, mosses, and, more rarely, upon 

 perennial leaves. In large forests they hang as a dense growth 

 from the trees (L^snea), but in other cases they encrust the rough 

 bark of the trees. They may also occur on the smooth bark of 

 young trees or shrubs, and sometimes on decayed or decaying 

 wood. All of these are classed as corticolous lichens. Saxicolous 

 lichens grow on rocks and stones, which they disintegrate. They 

 comprise the calcicolous forms, growing on limestones, or other cal- 

 careous rocks, on the mortar of walls, ets., and calcifugous forms 

 which grow on rocks of non-calcareous character. Terrestrial 

 lichens grow on all kinds of soil, some preferring peaty, some cal- 

 careous, some sandy, and some granitic soil, but none grow on 

 cultivated soil. 



Muscicolous lichens grow on decaying moss, such as the dead 

 peat mosses, while epiphyllous species grow on perennial leaves, 

 whose vitality they do not affect. The distribution of lichens is 

 greater than that of any other class of plant, occurring from the 

 poles to the equator, practically wherever land exists. Lichens 

 may be dried so thoroughly that they can easily be reduced to 

 powder, yet their vitality is only suspended, and moisture will 

 restore them to renewed activity. Their growth is extremely slow, 

 and the life of the plant seems to be very lotig, in some cases many 

 hundreds of years, 



Bryophyta and Pteridophyta. 



These are wholly absent from the sea, but in fresh water a 

 few bryophytes are known. The peat-moss (Sphagnum) grows 

 abundantly in wet woods or in bogs. The growing ends increase 

 while the old portion dies off. Among the pteridophytes the class 

 of Filicinse has an aquatic group in the rhizocarps, or water ferns 

 (Hydropterideae), which grow partly submerged or floating. The 

 spores of these plants are widely distributed by flotation and 



