GONIDIA OF LICHENS. 37 



M. Bornct passes in review the principal genera of the Algae which 

 he meets with in Lichens. In the first place he examines such as 

 contain chlorophyl [Trcntepohlia. Phyllactidium^ Protococcus), and 

 in the second place those which contain phycochrome (Scytonema, 

 SUgonemct) Nostoc, Glcrocapsa). 



Algse coloured by Chlorophyl. Trcntepohlia, Mart, comprises 

 small algae of the group Conferva, branched like Cladophora, from 

 which they are chiefly distinguished by not inhabiting water. They 

 arc universally distributed on bark, wood, rocks, and mosses, attain- 

 ing their greatesl development in moist and shady places. Their 

 beautiful orange colour, which becomes grey when kept for some 

 time in the herbarium, their odour of violets, or rather of Cantha- 

 rellus cibarius, which they retain after keeping, make them easy of 

 recognition. The great resemblance of Trentepohlia umbrina to the 

 gonidia of several Graphidece and Verrucarice has been recognised 

 by M. de Bary. M. Schwendener has confirmed the fact, and 

 mentions moreover the genus Roccella, as offering the same pecu- 

 liarity. M. Bornet has traced this resemblance in 13 genera of 

 Lichens : — (1.) Roccella tinctoria, Ach., R. phycopsis, Ach., R.juci- 

 formis, Ach. (2.) Lecanora, Ach. (sp. plnr.). (3.) Dirina re- 

 panda, Nyl. (4.) Ccenogonium Linkii, Ehrnb., C. confervoides, 

 Nyl. (5.) Byssocaulonnivewn, Montg. (6.) Lecidea lutea, Schaer, 

 L. microspetma, Nyl. (7.) Graphis elegans, Ach., G. contexta, 

 Pers., G. heterospora, Nyl. (8.) Opegrapha varia, Pers., 0. her- 

 harum, Montg. (9.) Stiymatidium crassum, Duby. (10.) Arthonia 

 cinnabarma,WaHl. (11.) Melaspileaarthomoides,Nj\. (12.) Chio- 

 decton myrticola, Fee., C. nigrocinctum, Montg. (13.) Vermcaria 

 nitida, Schrad. 



It would be premature to make a list of species of Trentepohlia 

 found associated with lichens, the species being as yet ill -defined, 

 and the lichens themselves too imperfectly known, as regards this 

 enquiry, to do so with sufficient precision. It is nevertheless cer- 

 tain that different species furnish gonidia to lichens, some of the 

 gonidia having more or less affinity with Trentepohlia umbrina, 

 under which name they may be provisionally placed. 



If a section of the bark be made on which grows Opegraplia 

 varia, Pers., selecting the part where the white stain of the 

 thallua is not very conspicuous, the thallus will be seen to be com- 

 posed of a loosely compacted tissue of filaments and yellow oval 

 gonidia containing red-brown granules. On careful examination 

 the hypha will be seen to extend beyond the apparent thallus, the 

 threads diminishing in quantity, so that isolated fibres may be traced, 



In the same part of the bark other filaments may be seen — of a 

 transparent green, much larger than the hypha, formed of cells 

 placed end to end, lightly attached at each articulation. The 

 arrangement of these cells and the mode of their increase show 

 thai they belong to Trentepohlia. On the confines of these two 

 vegetations we meet with some spaces where the hypha and the 



