The Status of the Algo-Lichen Hypothesis. ? 
produced zoospores. These in time developed into unicellular algje, 
and by judicious management they produced several generations. 
Although they drew difEerent ideas from this the Scliwendenerians 
immediately took this as an argument for the dualism of lichens. 
Later (1872) Woronin confirmed the observations of Famentzinand 
Barentzky by his own experiments made with Parmelia pulverulenta. 
When Schwendener propounded his theory one of the first to 
accept it was E. Bornet. He immediately began a series of obser- 
vations and experiments to prove it. In his treatment of this sub- 
ject {An. de Sc. Nat., vol. 17, ser. 5) he divides his observatioris 
into two divisions corresponding to those of Schwendener — i.e., 
those made upon lichens with chlorophyll-bearing gonidia, and lich- 
ens with phycochrome-bearing gonidia. Under the chlorophyll - 
bearing gonidia he found those belonging to such genera as Tren 
tepohlia, Phyllactidium, Protococcus, Cystococcus, Pleurococcus, etc. 
He found the gonidia of several of the Opegraphse, as 0. varia, to b& 
Trentepohlia. The branches of the alga were found ramifying the 
tissues of the bark, frequently going so far that the hyph^ of the 
lichen-fungus could not follow them. As they near the outer sur- 
face of the bark the hyphae and algae became more and more inter- 
laced until they reached the thallus proper. When studied at aU 
ages of the thallus the nature of the relations between the two were 
easily seen to be such as to preclude every chance of the one being 
developed from the other. The study of other lichens with simi- 
lar gonidia, as Verrucaria nitida, Rocella phycopsiSyChiodectoii nigro- 
cinctum, etc., led to the same conclusions. 
The gonidia of Opeg. felicina he found to be a Phyllactidium. The 
broad thallus of this alga was so large that the hyphae did not en- 
tirely envelop it, but by gradually branching, surrounded parts of it 
and even sent small branches into it. He found in an old thallus 
of Opegrapha varia the normal filaments of Trentepohlia together 
with sporangia, showing that it could not be the "first stage of the 
lichens," but was an entirely separate plant. He sowed the spores 
of Physcia {Theloschistes) parietina on Protococcus viridis, and 
found that the hyphae of the germinating spores readily enveloped 
the algae, and did not envelop any other objects with which they 
came in contact. He also sowed spores apart from the algae, and 
although germinating and producing hyphae as did the others, they 
produced no gonidia and died as soon as the nourishment from the 
spore was consumed. He obtained similar results with Biatora 
muscorum. 
