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XVI—On the Phenomena of Variegation and Cell-Multiplication in a Species 
of Enteromorpha. By P. Geppss, F.R.S.E., Demonstrator of Vegetable 
Histology in the University of Edinburgh. (Plate XIII.) 
(Received 4th April. Read 17th May 1880,) 
In the autumn of 1877 I found on stones in a sea-water aquarium in 
Professor Hux ey’s laboratory at South Kensington, the curious little Alga 
which forms the subject of the present paper. I have ever since kept speci- 
mens growing, carried them with me to various places in Britain and on the 
Continent, and subjected them to frequent examination at all seasons of the 
year. Dr Borner has kindly identified it for me as a species of Enteromorpha. 
Viewed with a lens, the fronds are of a beautiful green, often more or less 
mottled with white. Examination of such specimens with a somewhat higher 
power (say 1 inch) shows among the ordinary green cells others which are 
smaller and colourless, occurring singly or in patches of very variable size. 
Oftener than these variegations of the frond itself, one notices buds, or even 
large branches, which are completely colourless. And the extreme case—of 
large fronds, and indeed whole tufts, almost without any green cells, is not 
wanting. How are these phenomena to be accounted for ? 
The first hypothesis which suggests itself is that here we have an etiolation 
of green cells,—a mere blanching of particular cells or fronds, due to the 
interception of the light by the felt-work of Oscillatoriw, Conferve, &c., by 
which the specimens were always more or less thickly surrounded. But it will 
_ be seen from an inspection of the plate that the colourless cells are oftenest 
apical ; and when a fragment of the very thickest part of this vegetable felt is 
detached and viewed under the simple microscope, colourless shoots are to 
be seen projecting clear above the tangled mass of other Alge, while the 
portion of the frond thus shaded may be of the deepest green. Moreover, 
specimens kept growing for months in a window, exposed to direct sunlight 
for several hours daily, never lost their variegated aspect. A crucial experi- 
ment enabled me finally to exclude the hypothesis of a mere etiolation of 
normally green cells by deficiency of light. A flint covered with an abundant 
crop of the Alga under examination was broken into three pieces, of which one 
was exposed to sunshine for six or seven hours a day, another kept in the 
diffuse light of my workroom, and another placed in darkness. After the lapse 
of three or four weeks no change was appreciable. On the stone exposed to 
VOL. XXIX. PART II. 7A 
