4 The Status of the Algo-Lichen Hypothesis. 
As to those lichens containing phycochromgonidia, he found 
that Colothrix furnished gonidia for LicMna pygnma and conpiis; 
Scytonema and Lyngbya were found in such genera as Pannaria, 
Erioderma, and Stereocaulon (Cephalodia); Nostoc was found in Col- 
lema and allied genera; Etigonemain Ephebe, Spilonema, etc. ; and 
Gloeocapsain Synallisa, Cora, Omphalaria, and similar genera. Some- 
times he found the alga to be very little changed by the parasitism 
as in Ephebe and Spilonema; at others they were so changed as to be 
recognized only with difficulty. Two modes of contact were noticed : 
1. AVhere the hyphae are applied simply to the surface of the algae, as 
in Peltigera, Stictina, etc. 2. Where the hyphai branches enter the 
algal cells, as in Physcia, Omphalaria, etc. From these observations 
he draws the following conclusions: that since Trentepohlia, Phyllac- 
tidium, etc., are so complex in their nature, and since no instance 
of the hyphae enlarging and producing them has been found, and 
since these algae (Phyllactidium, Trentepohlia, Nostoc, Protococcus, 
etc.) are found in the free state, there can be no doubt of the dual 
nature of those lichens containing them, and that, 1st, all gonidia 
can be referred to some algal type; and, 2d, the relations between 
hyphaj and gonidia are such as to exclude all possibility of one be- 
ing produced from the other, and the theory of parasitism alone can 
explain these relations satisfactorily. 
Reess made a series of cultivations with spores of Collema glances- 
cetis sown with Nostoc lichenoides. By careful manipulation he 
produced a complete Collema thallus, but lacking the fruits. He saw 
the germinating spores " send out hyphae which branched and 
forced themselves into the Nostoc." 
Treub used the gonidia of one species of lichen and the sporqs of 
another. His success was similar to that of Keess 
Stalil uses the hymeneal gonidia and spores of Endocarpon pusil- 
lum and spores of Tlielidium minutulum. He succeeded in produ- 
cing a fully developed thallus, showing that these hymenial gonidia 
are ejected at the same time as the spores, to serve as gonidia for the 
young plants. He cultivated these hymenial gonidia separately, and 
found them to grow and divide just as do the undoubted unicellular 
algae. Lately Bounier has succeeded in producing a complete lichen 
tliallus with mature fruits by using lichen spores and algae. 
Among the botanists in the United States who have favored 
Schwendenerism in their later works arie Dr. Asa Gray, Dr. Bessey, 
H. Willy, etc. 
Most of the Eaglish lichenologists, together with Koerber, Nyland- 
