26 



On the high exposed rocks of our hills, and in mountainous 

 districts, the rock Lichens attain their highest development, 

 always growing on sites most exposed to the storms of rain ; and 

 the frequent damp mists of the upland districts help to sustain 

 these epiphytal vegetable organisms. Those that grow on the 

 trunks of trees in lower districts prefer trees growing in hedge- 

 rows, or exposed trees at the outskirts of plantations, always 

 fixing themselves on the side most exposed to the prevailing 

 rain storms of the district. 



Lichens are very tenacious of life, and may be completely 

 dried up without losing their vitality. 



Fungi. — The greater number of the Fungi are parasitical (not 

 epiphytal), deriving their support in a great measure from the 

 host on which they grow. Some of the larger forms, in the 

 family of Agarics, of which the well-known mushroom is a 

 typical species, grow in humus, or soil, that contains decaying 

 vegetable or animal matter. Some grow on the living bark of 

 trees, their mycelium penetrating the tissues of the wood itself ; 

 and smaller forms of the Fungi grow on fallen leaves and decay- 

 ingbranches, assisting in the destruction of these. 



A very large number of minute microscopical Fungi grow as 

 true parasites upon living vegetable and animal organisms, and 

 when atmospheric or other influences occur to assist their de- 

 velopment, they become very destructive to the hosts upon 

 which they grow. The potato disease, vine mildew, dry rot 

 fungus, etc., etc., may be named as well-known results of their 

 destructive parasitic growth on the organisms attacked. The 

 ringworm on the human skin is also known to be the result of the 

 growth of a minute parasitical fungus. The Fungi are very 

 numerous, and are classified and arranged into many divisions, 

 and far exceed in numbers the whole of the flowering or Phanerog- 

 amous plants in the British Islands. They require a microscope 

 for their proper stud}', and we may refer students of them to the 

 works of Berkeley, W. G. Smith, Dr. Cooke, G. Massee, and 

 other British writers on them, Tulasne in France, De Bary 

 in Germany, and many others who have by their researches 

 much increased the knowledge of these vegetable parasites. 



Recently students of the minute Fungi have been tracing out that 

 several of them pass through different cycles of growth, assum- 

 ing one form upon one host plant, and in their next stage of 



