THALLOPHVTES, 
Rye, or of other nearly allied grasses, Kühn states that the sphacelia arises from them, 
and the cycle of development is thus completed. 
(6) Lichens^ From the researches of Schwendener^, there can no longer be any 
doubt that the Lichens are true Fungi belonging to the Ascomycetes (Discomycetes 
and Pyrenomycetes), but distinguished by a singular parasitism. Their hosts are Algae, 
which grow normally in damp places but not actually in water, and belong, moreover, 
to very various groups (rarely Confervacese, frequently Chroococcaceae and Nostocaceae, 
more often Palmellaceae, sometimes Chroolepideae). The Fungi themselves (Lichen- 
forming Fungi) are not found in any other form than as parasites on Algae ; while the 
Algae which are attacked by them, and which, when combined with the Fungus, are 
called Gonidia, are known in the free condition without the Fungus. When the species 
attacked by the Lichen-fungus is a filamentous Alga, and the development of the 
hyphal tissue is only moderate (as in Ephebe and Ccenogonium), the true state of the 
case is at once clear; and as Lichens of this kind have become better known, the 
suspicion has frequently arisen that they are in fact only Algae infested by Fungi. 
In the Collemaceae also attention has frequently been drawn to the identity of the 
gonidia with the moniliform filaments of Nostocaceae ; but in this case the nourishing Alga 
usually undergoes considerable changes of habit, at least in its external contour, from 
the influence of the parasitic Fungus, like Euphorbia Cyparissias from its parasitic 
J^cidium. But the greater number of Lichen-fungi prefer as hosts the Ghroococcaceae 
and Palmellaceae which grow as stains and incrustations on damp ground, the bark 
of trees, and stones. The separate cells and groups of cells of these Algae become so 
involved by the tissue of the Fungus, that they are at last only interspersed here and 
there in the dense hyphal tissue, or appear in it as a special layer (the gonidial layer). 
The growth and multiplication of these Algae, which thus become entirely enclosed by 
their parasites, is not hindered, but their development is disturbed in other ways. When, 
however, they are freed from their enclosing Fungus-tissue, their normal development 
proceeds, and in a few cases even the formation of zoogonidia takes place in them, 
^ Tulasne, Memoire pour servir ä Thistoire organographique et physiologique des Lichens 
(Annales des Sei. Nat. 3rd series, vol. XVII). — Schwendener, Untersuchungen über den Flechten- 
thallus (in Nägeli's Beiträge zur wissensch. Botanik, i860 and 1862. — Ditto, Laub- u. Gallertflechten 
(Nägeli's Beiträge zur wissensch. Botanik. 1868). — Ditto, Flora, 1872, nos, 11-15. — Stahl, Beit. z. 
Entwickel.-Gesch. der Flechten, 1877. [Quart. Journ. Micr. Sc. 1873, P- 235, and 1878, pp. 
144. 438.] 
^ [The views of Schwendener have been corroborated by Bornet in an elaborate memoir pub- 
lished in the Ann. des Sei. Nat. 1873, vol. XVII. He also put them to a synihetical test by sowing 
the spores of Parmelia parietina upon Protococcus. About the fifteenth day the hyphse were well 
developed and ramified. Wherever they met isolated cells of Protococcus or groups of them, 
they attached themselves either directly or by means of a lateral branch. They did this, to the 
Protococcus only, neglecting altogether the other bodies which were mixed with it. Similar results 
were obtained when the spores of Biatora muscorum were sown upon Protococcus. Spores of 
Parmelia sown separately ramified much less and developed no chlorophyll ; Protococcus, on the 
other hand, during the same period remained unchanged and put out no hyphae. Tulasne, however, 
sowed the spores of Lichens and believed that he twice detected the formation of gonidia upon the 
hyphae (Ann. des Sei. Nat. 1852, XVII, pp. 96-98). De Bary indeed described the green gonidium 
as originating by the expansion of a short lateral branch of the hypha into a globular cell, which 
is shut off by a septum and assumes a green colour ; once formed, it increases independently by 
division, and a number of the gonidia eventually lie without stipites in the interstices of the 
Lichen-tissue (Morph, u. Phys. der Pilze, pp. 258, 263-265). Berkeley also believes that the 
gonidia originate from the hyphse. having had ' a good opportunity of ascertaining their development 
from the threads of the mycelium in specimens developed within the vessels of pine wood ' (Introd. 
to Crypt. Bot. p. 373). For a careful resume of all the recent literature of the subject by Archer, 
see Quart. Journ, Micr. Sc. 1873, p. 217. In this country Bentham has criticised Schwendener's 
view (Address to Lin. Soc. May 23, 1873), ^^^d Thwaites and Berkeley have also expressed their 
dissent (Gard. Chron. 1873, p. 1341).] 
