ALGA GROWING ON THE EUROPEAN TORTOISE. 251 
Figs. 7 a, b, c. Callitriche verna. Leaf-cells from a plant deprived of light for 
ten days: a, from middle part of leaf, grains in simple negative apos- 
trophe ; dand c, from near their tip, the effect of darkness now more 
pronounced, the grains having massed. 
Fig. 8. Eschscholtzia californica, Palisade-cells, seen from above after eleven 
days in the dark ; the grains are closely massed. 
Figs. 9 a & b. Eschscholtzia californica. Palisade-cells, in section, after 
twelve days’ darkness; the right-hand cell of fig. 9 b is a mesophyll 
cell. 
Fig. 10. Epidermal cell of the frond of Pteris serrulata, showing the effect 
upon the disposition of the chlorophyll of three weeks’ withholding of 
light: p, a grain tilted up on to its edge by the pressure of ite 
‘neighbours. 
Figs. 11 a, 4, c. A small portion of a prothallus of probably a species of 
Adiantum: a, grains moving into apostrophe under the influence 
of sunlight; 5, commencing epistrophe after half an hour in the 
shade; c, epistrophe still further advanced, one of the grains in the 
left-hand cell still forced up into profile by its fellows. 
Fig. 12. From a Funaria hygrometrica leaf set in sunlight, the grains making 
for the wall, which some have reached: p, a grain turned up on 
its edge after abutting on another already against the side-wall. 
Fig. 13. Part of a barrel-shaped cell from the leaf of Echeveria metallica grow- 
ing in low diffused light; two of the grains in the centre of the 
clump tilted up on to their edge. 
Fig. 14. Top of cell of an Zlodea-leaf with rotating protoplasm: =, grain about 
to change profile for broadside position. 
Note on an Alga (Dermatophyton radicans, r) growing on 
the European Tortoise. By M. C. Porn, M.A., F.LS., 
Assistant Curator of the University Herbarium, Cambridge. 
{Read 2nd June, 1887.] 
(Puate VIII.) 
Tux alga which is the subject of this paper is found growing 
principally upon the dorsal surface of the carapace of the water 
tortoise (Olemmys caspica), which inhabits the southern ‘parts of 
Europe, and, by spending a great part of its existence in water, 
offers its back as a suitable nidus for alge. l 
The alga appears to the naked eye as irregular but roundish 
dark-green patches which vary very much in size, often having a 
diameter of about a quarter of an inch, as ata, fig.1, Pl. VIII. On 
