The Origin and Nature of Lichens 



ascus) in organs of various shapes, knobs, or flat disks (apothe- 

 cia), or cup and flask-like cavities (perithecia). In addition to 

 these large spores (ascospores) of the knobs and cups there are 

 smaller spores (conidia) 

 produced in smaller cavi- 

 ties scattered over the thal- 

 lus. There is much conjee- 

 ture as to what may be the 

 function of these spores. 

 In tropical countries there 



is found a very beautiful 



fanlike, greenish - yellow 

 lichen (Cora pavonia) hav- 

 ing a thallus marked with 

 concentric ridges. This 

 lichen bears its spores on 

 the under surface on tiny 

 clubs (basidia) instead of 

 in sacs. The algal partner 

 is one of the unicellular 

 blue-green algae (Chroococ- 

 cus) often found in muci- 

 laginous masses in damp 



m 



A 



Usnea barbate, (Fr.) (A) A vertical section 

 places. Another tropical through a strand of the Bchen. 



r . (B) A cross section of a strand at a point where 



form ( LJlCtyOncma) grOWS a radiating strand was cut in vertical section 

 35 delicate blue-green, felt- ($) Apex of strand, (r) cortex, (g) algae, (m) pith 



layer, (*) a central card, (sa) section of a radiating 

 like plates Standing OUt branch with its central cord, (*). 



from the tree-branches to 



to which they are attached. The algal partner in this case is a 

 blue-green, branching, and thread-like species (Scytonema) found 

 enveloped in a mucilaginous mass in fresh water. The fungus- 

 partner in both the Cora pa-vonia and the Dictyonema is one of 

 the group which forms leathery crusts on twigs and tree trunks. 



Another lichen, Laudatea, has the same partners as the Dic- 

 tyonema. It is a crustaceous form and in it we find the exception 

 to the rule, that the fungus is the leading member of the lichen 

 firm. In it the alga has the upper hand and determines the 

 direction of the growth. 



One lichen (Emericella vartecolour), which resembles a 

 tiny puff-ball, is known to be due to the confederacy of a 



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