40 



GONIDIA OF LICHENS. 



into the frond itself, that is into the interior of the case, or 

 gelatine, which unites the cells together. 



Amongst those lichens enumerated, in which the hypha applies 

 itself to the surface of the alga, may be mentioned Stereocaulon 

 ramulosum, Sw., the cephalodia of which were found by M. Bornet 

 on dissection to contain long flexuous filaments of the character of 

 Scytonema, which had been taken up and encompassed by the hypha ; 

 also Coccocarpia molybdea, Pers., in the young fronds of which were 

 found moniliform gonidia, disposed in long parallel threads, in 

 which it was impossible to avoid recognizing the similarity to a 

 Scytonema, such as were found scattered upon the bark on which 

 the lichen had grown. 



Amongst the lichens he mentions in which the hypha penetrates 

 into the interior of the alga, we have only space for one species, 

 viz., Arnoldia minutula, Born. (sp. nov.) This lichen is very small, 

 scarcely visible to the naked eye, pyriform or oblong, growing on 

 the ground. On examining a thin section, the chaplets are seen 

 to present here and there (independent of the heterocysts) some 

 cells much larger than others, surrounded by a thick membrane. 

 To each of these cells is fixed a short filament, a part of the 

 general network of the hypha. The modification which these 

 cells experience, shows the contact between them and the extremity 

 of the inserted filament is not accidental, but that the hypha exer- 

 cises on the gonidia an energetic action. Under its influence the 

 cell becomes much enlarged, and surrounded with a thick mem- 

 brane, which the ordinary cells do not possess ; this is followed by 

 a change in the colouring matter, which separates into a grumous 

 mass in a colourless fluid, and the side of the cell opposite the 

 point of attachment shrivels up, till the gonidium becomes a mere 

 dead membrane. These phenomena begin the moment the ex- 

 tremity of a hypha-filament comes in contact with an algal- 

 cell. 



In conclusion, M. Bornet considers he has established the two 

 following propositions : — 



1. Every gonidium of a lichen may be referred to a species of 

 Alga. 



2. The connexion of the hypha with the gonidia is of such a 

 nature as to exclude all possibility of one organism being produced 

 from the other, and that the theory of parasitism can alone explain 

 it satisfactorily. 



M. Bornet's Paper is illustrated with eleven coloured plates of 

 microscopical dissections which assist very considerably the eluci- 

 dation of his theory. 



Woolhope Naturalists' Field Club. — The annual meeting 

 of this Club, which is devoted to Fungology, will be held at Here- 

 ford, on Tuesday, 14th October, 1873. 



