LICHEN HYPHAE 51 



normally find place, and above that a second compact tissue, or outer cortex, 

 from which arose the aerial hyphae. The culture could not be prolonged 

 more than eight months. 



D. CONTINUITY OF PROTOPLASM IN HYPHAL CELLS 



Wahrlich 1 demonstrated that continuity of protoplasm was as constant 

 between the cells of fungi as it has been proved to be between the cells of 

 the higher plants. His researches included the hyphae of the lichens, Cla- 

 donia fimbriata and Physcia (Xanthorid) parietina. 



Baur 2 and Darbishire 3 found independently that an open connection 

 existed between the cells of the carpogonial structures in the lichens they 

 examined. The subject as regards the thalline hyphae was again taken up 

 by Kienitz-Gerloff 4 who obtained his best results in the hypothecial tissue 

 of Peltigera canina and P. polydactyla. Most of the cross septa showed one 

 central protoplasmic strand traversing the wall from cell to cell, but in some 

 instances there were as many as four to six pits in the walls. The thickening 

 of the cell-walls is uneven and projects variously into the cavity of the cell. 

 Meyer's 8 work was equally conclusive: all the cells of an individual hypha, 

 he found, are in protoplasmic connection ; and in plectenchymatous tissue 

 the side walls are frequently perforated. Cell-fusions due to anastomosis are 

 frequent in lichen hyphae, and the wall at or near the point effusion is also 

 traversed by a thread of protoplasm, though such connections are regarded 

 as adventitious. Fusions with plasma connections are numerous in the 

 matted hairs on the upper surface of Peltigera canina and they also occur 

 between the hyphae forming the rhizoids of that lichen. The work of Salter 6 

 may also be noted. He claimed that his researches tended to show complete 

 anatomical union between all the tissues of the lichen plant, not only between 

 the hyphae of the various tissues but also between hyphae and gonidia. 



III. LICHEN ALGAE 



A. TYPES OF ALGAE 



. The algal constituents of the lichen thallus belong to the two classes, 

 Myxophyceae, generally termed blue-green algae, and Chlorophyceae which 

 are coloured bright-green or yellow-green. Most of them are land forms, 

 and, in a free condition, they inhabit moist or shady situations, tree-trunks, 

 walls, etc. They multiply by division or by sporulation within the thallus; 

 zoospores are never formed except in open cultivation. The determination 

 of the genera and species to which the lichen algae severally belong is often 

 uncertain, but their distribution within the lichen kingdom is as follows : 



1 Wahrlich 1893. 2 Baur 1898. 3 Darbishire 1899. 



4 Kienitz-Gerloff 1902. 5 Meyer 1902. 6 Salter 1902. 



42 



