240 PLANT LIFE. 



leaves, etc., on the ground. They are made up of 

 fungus-filaments woven or united together, and repre- 

 sent the absorbing system. These absorbing rhizines 

 vary greatly in structure and functions. In some of 

 the other lichens, owing to the peculiar conditions 

 of their life, pieces may be torn away by wind. If 

 these pieces come in contact with a stone or, perhaps, 

 the bark of a tree, special grappling rhizines are formed, 

 which fix themselves to the support. They grow out 

 from the lichen at right angles to its stem, and are very 

 rapidly formed. They even increase in length and 

 thickness after they are attached. They are well 

 adapted to hold on to a support, as the fungus threads 

 of which they are composed run lengthwise, and are 

 thick-walled. If accidentally broken off, new grappling 

 rhizines may be produced. 



Sometimes different species of Cladonia, or even 

 different lobes of the same plant, may grow together 

 and anastomose. The younger lobes are also often 

 parasitic upon the older ones, as may be seen in 

 Parmelia saxatilis. On examining a cross section of 

 Peltlgera canina with the microscope, it is easy to see 

 that the upper surface of the lichen is made up of 

 fungus threads firmly joined together. Probably the 

 cell walls of those threads stick together by a change 

 of their outer surface into some gelatinous or gummy 

 modification {inucose variety) of the cellulose. The 

 lower surface is not so distinct ; it is, indeed, interrupted, 

 and not continuous. The central part of the lichen 

 consists of loose entangled fungus threads, and the 

 algal cells are arranged in an irregular layer amongst 

 these threads and near the upper surface, where, of 

 course, they will be near the light. It has recently 

 been shown by Dr. Salter that all the living parts 



