GENERAL CHARACTERS OF BRITISH LICHENS. 65 



contents, most usually brown, which are sometimes coarse 

 and granular. It was formerly generally supposed that these 

 bodies were simple filaments or tubes, undivided by septa 

 and devoid of contents ; but the application of sulphuric 

 acid or iodine under the microscope, by rendering evident 

 the septa of the constituent cells and coagulating or colour- 

 ing their contents, proves this opinion to be fallacious. Some 

 theorists have described the paraphyses as prolongations or 

 modifications of the filaments of the medullary layer of the 

 thallus ; others have regarded them as rudimentary, sterile, 

 or abortive thecse. The former theory is proved to be erro- 

 neous, by their having been found by the latest observers to 

 arise from the hypothecial cells, as already stated ; the latter 

 equally so by the consideration that they precede the thecse 

 in the order of development, and possess ah initio a distinct 

 structure, and apparently a distinct function. 



The Theca, which may be regarded as the parent cells of 

 the spores, are amylaceous, membranous sacs, varying much 

 in size and shape, but always inferior in length — and greatly 

 superior in breadth — to the paraphyses, and usually either 

 of an obovate, ellipsoid, linear, or clavate form, the superior 

 extremity being dilated and obtuse, the inferior tapering 

 suddenly or gradually into a narrow pedicle or filament. 



p 



