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Pellia epiphylla, (L.) Corda. 
thallus, and the difficulty of isolating it, point to such a relationship. The 
fungus evidently finds the liverwort a very favourable substratum, as indicated 
by the considerable number of fungal hyphae found in some material, 
branching profusely, and ramifying through the tissue in all directions, and 
obtaining food material from the cells into which they have penetrated. 
The plant is to some extent unharmed — at least it can go on growing 
and reproducing in the normal manner. Whether the fungus is of any 
actual use to the liverwort is at present uncertain. Upon entering the 
thallus the fungus seems to sever its connexion with the soil, so that it is 
unlikely that the association is a mycorhiza. 
Whatever may be the relationship, it seems probable that the fungus 
is the dominant partner, obtaining its food material from the liverwort, 
damaging it to a certain extent by killing the cells which it enters ; but 
the liverwort, in most cases, still retains the power of growth and 
reproduction. 
In a few instances, however, the association becomes of the nature of 
a disease. Here the cells are quite brown in colour ; the thallus in con- 
sequence, instead of appearing green, is dark brown, and incapable of 
further development. 
The Sporophyte. In the sporophyte the effect of the fungus is much 
more drastic than in the gametophyte. The fungus has a twofold effect 
upon the tissues. The cells are turned brown in colour, the chloroplastids 
are destroyed, and the cells are ultimately killed. Secondly, the cell-walls 
partially disappear ; this is especially noticeable in the capsule-wall, where 
only the thickened walls of the cells are left whole, the thin walls being 
very indistinct or completely absent. The young gametophytes also are 
killed or prevented from reaching their full development. Their cell-walls 
are partially or completely absorbed, and the chloroplastids are discoloured"? 
and all attempts to make them germinate, even when fully developed, have 
failed, whereas similar spores from healthy capsules germinated readily on 
a synthetic agar medium. Moreover, the whole tissue of the sporophyte 
becomes infected, as there is no definite zone which remains free of hyphae, 
as in the upper layers of cells in the gametophyte. 
The cell-walls of the sporophyte did not respond to the test for 
sphagnol. 
The relationship between the fungus and the sporophyte is obviously 
not one of symbiosis : in this generation of Pellia the fungus is a disease, 
killing the tissues and rendering them incapable of maturing. 
Summary. 
i. The cells of the thallus of Pellia epiphylla contain a fungus which 
occurs in a definite zone along the thickened median portion towards the 
ventral surface of the thallus and in the rhizoids. 
