46 Transactions British Mycological Society. 
The photomicrographs of microscope slides were voluntarily 
prepared by Mr J. H. Pledge, F.R.M.S., who had at his dis- 
posal, by permission of the management, the apparatus of the 
physical Iaboratory of the Kodak Company’s factory at Harrow. 
I take this occasion for expressing my grateful thanks to him 
for the great skill he displayed in this work. 
Having had the opportunity of discussing with Miss A. 
Lorrain Smith some of the matter brought forward im this 
communication, I thank her for valuable advice and criticism. 
NOTE. 
Since reading the above paper I have noted that the alga 
Protococcus is the gonidium of the lichens Dermatocarpon aqua- 
ticum and of D. miniatum. It is not so in the case of D. hepa- 
ticum and D. cinerewm. 
As regards the two former, the gonidium resembles in size, 
and in its mode of multiplication by binary fission, the free 
Protococcus obtained from the bark of trees, palings, etc. 
This alga has not been modified in shape and size to any 
appreciable extent on becoming the algal constituent of a 
lichen. 
DESCRIPTION OF PLATE I. 
Fig. 1. Eveyrnia prunastvi. Transverse section of the thallus showing gonidia 
arranged in spherical groups. x r000. 
Fig. 2. E. prunastvi. Normal gonidia showing variation in size of the cell 
according to age. Photograph especially developed to show cell-wall. 
x IOOO. 
Fig. 3. E. prunastrvi. Normal and sporulating gonidia. Some are undergoing 
changes previous to sporulation. x 1000. 
Fig. 4. E. prunastvi. An isolated gonidium containing sixteen daughter- 
gonidia, not fully developed. x rooo. 
Fig. 5. E. prunastri. An isolated gonidium containing sixteen fully developed 
daughter-gonidia. The mother cell-wall has partly disappeared. x 1000. 
Fig. 6. Cladonia digitata. A group of liberated daughter-gonidia, invaded by 
hyphae, being forced apart. Two twin-gonidia are on the left. x 1000. 
LIST OF PAPERS AND PUBLICATIONS QUOTED. 
(1) De Bary, A.—Comparative Morphology and Biology of the Fungi, etc. 
Oxford (1887). 
(2) Bornet, E.—Recherches sur les Gonidies de Lichens. Ann. d. Sci. Nat. 
5th Série, xviI (1873). 
(3) CHopaT, R.—Matériaux pour la Flore Cryptogamique Suisse, vol. Iv, 
fasc. 2 (1913). 
(4) Dantrov, A. N.—Ueber das gegenseitige Verhaltnis zwischen den 
Gonidien und den Pilzkomponenten in der Flechten Symbiose. Bull. 
Jard. Imp. Bot. St Pétersbourg, tom. x, livr. 2 (1910). Translation Journ. 
Bot. July 1918. 
(5) Famintzin, A. and BaRANETzKy, J.—Beitrag zur Entwickelungs- 
geschichte der Gonidien- und Zoosporen-Bildung bei Physcia parietina. 
Bot. Zeit. (1867), 189-190. Mémoires de 1l’Acad. St Pétersbourg, vit, 
Série 11 (1868). 
