AND LIFE-HISTORY OF A TROPICAL EPIPHYLLOUS LICHEN. 113) 
type, along similar lines to those followed, for instance, in comparing Coleochete divergens 
and 6. scutata, or in deducing any more compound type from a simple one. 
This mode of viewing the question seems to throw light on some other points of 
interest. Bornet, in his remarkable researches on the Gonidia of Lichens *, has shown 
that the genus Opegrapha consists of a Fungus-invested Alga which he refers to two 
genera. Тһе gonidial layer of Opegrapha varia is, in his opinion, a Trentepohlia, while 
that of О. filicina must be referred to Phyllactidium. Не also shows that Trentepohlia 
enters into the constitution of several other Lichens (Verrucaria, Roccella, Chio- 
decton, “ Byssocaulon,” “ Caenogonium,” &c.)+. Now the genus Trentepohlia, founded 
by Martius, is sunk in Chroolepus, Ag., although Bornet wished to preserve the old 
name. The genus founded by Kiitzing under ни name of Phyllactidium is merged in 
Coleochete by Pringsheim }. 
From these considerations it: is evident that, in the first place, such А16 as I have 
described have already been recognized аз Ше gonidia of Lichens, and, secondly, that a 
considerable amount of uncertainty exists as to the exact relationships of the genera. 
Bornet, in his second note on the gonidia of Lichens §, describes old specimens of 
Opegrapha varia, in which were found filaments of the Trentepohlia (Chroolepus) 
bearing sporanges, from which zoospores escaped through projecting ostiola: many 
zoospores were also found in the water. 
Millardet, in 1866, discovered an epiphyllous Alga on Abies pectinata, which he named 
Phycopeltis epiphyton |. I have seen one of the original specimens of this form, through 
the kindness of my friend Prof. de Bary § ; and there is sufficient resemblance between 
it and the tropical Alga (especially the young states of the latter) to encourage the hope 
that we may have representatives in Europe which can be studied in the living state. 
The Alga forms small discoid growths on the leaves of the damp lower branches. Its 
comparatively large cells are filled with orange-red oily matter; and certain of these 
become distinguished by their denser contents, which finally pass over into zoospores. 
These zoospores pass through a hole in the upper wall; and a comparison of Millardet’s 
fig. 31 with my figs. 42 and 49-52 is very suggestive. The liberated zoospores only move 
for about five minutes, and, after coming to rest, produce disks with orange-red contents 
as before. The law of growth is as described for Coleochete &c. ; and the cell series can be 
separated, forming loose branching filaments. On p. 46 Millardet states that he once 
only discovered an oogonium-like globule on a short pedicel inserted into the thallus. 
Viewed in the light of the described facts, I think we may probably expect that sub- 
sequent discoveries will establish a group of organisms having a similar relation to the 
* Ann. des бе. Nat. sér. 5% tom, xvii. p. 45, and tom. xix. p. 315. Вогпеб also points out that Kützing (Tab. 
Phye. pl. 97, vol. iv.) figures Chroolepus moniliformis with Fungus-hyphe invading it. 
Т Loe. cit.,and Sachs, Text-book, р. 329. Е t Loe. cit. 
§ Ann. des Sc. Nat. sér. 5% tom, xix. p. 315. 
|| Mém. dela Soc. des Sc. Nat. de Strasbourg, tom. vi. 1870, p. 42. 
4| De Bary also allowed me to see the specimen of PhAyllactidiwn found by Mettenius on Trichomanes elegans 
from Brazil. It is simply referred to by Mettenius (Abh. der math.-phys. Cl. der kónigl. süchs. Gesellsch. der 
Wiss. xi. p. 464) as a Coleochete-like form on Ferns. 
T 2 
