764 Proceedings of the Royal Irish Academy. 



TMs teing the case there is, of course, no question of lichen for- 

 mation. In the areas where the growth of Strigula is going on and 

 tlie spreading lichen is incorporating the yellow cells of Phycopeltis 

 expansa it sometimes lifts up the thallus of P. nigra and separates it 

 from the leaf, but has no physiological effect upon it. 



In parts it is true there occur circular dark areas with a central 

 aperture such as were observed by Mobius and Cunningham, and 

 regarded by them as possibly pycnidia. In the New Zealand speci- 

 mens, however, they are scarcely raised above the level of the 

 thallus ; the aperture is irregular, not like a true ostiole, and the 

 surrounding cells have no definite relation to it. I have not observed 

 any contents in these bodies, and am of opinion that they are only 

 regions in which the thallus has separated from the leaf surface, and 

 the cells in the centre have separated from each other and give 

 the appearance of an aperture. They have certainly a strong 

 resemblance to the conceptacles of simple forms of Melobesia ; but 

 no structures of this kind have been seen or are likely to occur in 

 any form of terrestrial algae : while the absence of hyphse prevents 

 one from regarding them as the pycnides of some fungus form. 



This absence of associated hyphse in the case of Phycopeltis nigra 

 should be looked upon not only as a mere negative characteristic of the 

 species, but as associated in some way with its peculiar colour. 



It may seem incredible that a plant of such a distinctively algal 

 type of structure should have a fungoid physiology ; but the fact that 

 its exceptional colour is associated with immunity from the attacks 

 of hyphae points to some great physiological difference between it and 

 the yellow species. 



BlBLIOGKA-PHY. 



1. Agaedh. — Systema Algarum. Lundse, 1824. 



2. Mahtius. — Flora cryptogamica Erlangen sis Norimbergse, 1817. 



3. MiLLAEDET. — Mem. Soc. Sci. Nat. Strasb., vi., 1870. 



4. KiJTZiNG. — Spec. Alg. Lipsise, 1849. 



5c Eeinsch. — Cent. ad. Algologiam et Fung. Lipsiae, 1875. 



6. Metienixts. — Abhandlung iiber die Hymenophyllaceen. 



7. BoENET. — Ann. Sci. Nat. (" Gonidies des Lichenes"), 1873. 



8. MoNTAGNE. — Flora Algerienne. 



9. Peingsheim. — Jahrbuch. Wiss. Bot., ii., 1860. 



10. Cunningham. — Trans. Linn. Soc. Bot., ser. 2, vol. i., 1877. 



