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MORPHOLOGY 



As cephalodia contain rather dark-coloured, blue-green algae, they are 

 nearly always noticeably darker than the thalli on which they grow, varying 

 from yellowish-red or brown in those of Lecanora gelida to pale-coloured in 



Fig. 76. Ricasolia amplissima de Not. (Lobaria laciniata Wain.) on oak, reduced. The dark 

 patches are tufts of branching cephalodia (A. Wilson, Photo.). 



Lecidea c0nsentiens\ a darker red in Lecidea panaeola and various shades 

 of green, grey or brown in Stereocaulon, Lobaria (Ricasolia), etc. They form 

 either flat expansions of varying size on the upper surface of the thallus, 

 rounded or wrinkled wart-like growths, or upright branching structures. 

 On the lower surface, where they are not unfrequent, they take the form of 

 small brown nodules or swellings. In a number of species packets of blue- 

 green algae surrounded by hyphae are found embedded in the thallus, 

 either in the pith or immediately under the cortex. They are of the same 

 nature as the superficial excrescences and are also regarded as cephalodia. 



1 Leighton 1869. 



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