46 CONSTITUENTS OF THE LICHEN THALLUS 



II. LICHEN HYPHAE 



A. Origin of Hyphae 



Lichen hyphae form the ground tissue of the thallus apart from the 

 gonidia or algal cells. They are septate branched filaments of single cell 

 rows and are colourless or may be tinged by pigments or lichen acids to 

 some shade of yellow, brown or black. They are of fungal nature, and are 

 produced by the mature lichen spore. 



The germination of the spore was probably first observed by Meyer^ 

 His account of the actual process is somewhat vague, and he misinterpreted 

 the subsequent development into thallus and fruit entirely for want of the 

 necessary magnification ; but that he did succeed in germinating the spores 

 is unquestionable. He cultivated them on a smooth surface and they grew 

 into a "dendritic formation" — a true hypothallus. Many years later the 

 development of hyphae from lichen spores was observed by HoUe^ who saw 

 and figured the process unmistakably in Borrera {Pkyscid) ciliaris. 



A series of spore cultures was undertaken by Tulasne^ with the twofold 

 object of discovering the exact origin of hyphae and gonidia and of their 

 relationship to each other. The results of his classical experiment with the 

 spores of Verrucaria muralis — as interpreted by him — were accepted by the 

 lichenologists of that time as conclusive evidence of the genetic origin of the 

 gonidia within the thallus. 



The spores of the lichen in large numbers had been sown by Tulasne 

 in early spring on the smooth polished surface of a piece of limestone, and 



Fig. 14. Germinating spores of Verrucaria muralis Ach. after two 

 months' culture x ca. 500 (after Tulasne). 



were covered with a watch-glass to protect them from dust, etc. At 

 irregular intervals they were moistened with water, and from time to time 



1 Meyer 1825. 2 Holle 1849. 3 Tulasne 1852. 



