ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 645 



Variegation and Cell-multiplication in a Species of Entero- 

 morpha.* — Mr. P. Geddes found on stones in a sea-water aquarium 

 in the laboratory at South Kensington, a curious little alga, identified 

 by Dr. Bornet as a species of Enter omorplia. 



Viewed with a lens, the fronds are of a beautiful green, often 

 more or less mottled with white, and a 1-iuch objective 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, completely colourless. And the extreme ease — of whole 

 tufts, almost without any green cells — is not wanting. 



These phenomena are not due to an etiolation of green cells, for 

 the colourless cells are oftenest apical, and colourless shoots are to be 

 seen projecting clear above the tangled mass of other Algae, by which 

 the specimens are always more or less surrounded, while the portion 

 of the frond thus shaded may be of the deepest green. Moreover, 

 specimens kept growing for months, exposed to direct sunlight for 

 several hours daily, never lost their variegated aspect ; nor did those 

 kept in darkness show any distinct increase in the proportion of 

 white cells to green. 



On a closer examination of the colourless buds, Mr. Geddes found 

 that, at one side of the frond or filament, and generally midway 

 between two green cells, there is often a slight prominence of 

 cellulose enclosing a tiny droplet of colourless, non-nucleated, hyaline 

 protoplasm. In a further stage are two similar but larger masses, 

 and so on up to a comparatively long row of colourless nucleated 

 cells, a series of gradations which shows that the colourless shoot 

 arises in a way totally distinct from that by which the ordinary green 

 cells are developed. The transparent cells multiply by transverse 

 division, and have also the power of developing chlorophyll. While 

 the majority of the colourless shoots are sharply marked off by their 

 colour and general appearance from the green part of the frond, others 

 are to be found in which there is a gentle gradation from white cells 

 to green, the development of chlorophyll beginning at the base of the 

 shoot, and proceeding upwards. The multiplication of the green 

 cells by transverse division is obvious ; but it is by no means easy 

 to account for the origin of the colourless cells. 



The cellulose of an Alga possesses a capsular structure. A cell 

 throws out a coat of cellulose, and then divides into two new cells ; 

 each developes its own investment of cellulose, and these lie end to end 

 within the first. The extremities of these new cells being biconvex, 

 they are not in complete apposition, but an angular interspace is left 

 which extends ring-fashion round the filament. It is not to be 

 expected that these laminaB of cellulose should be of precisely equal 

 thickness and strength throughout, nor of equal permeability to fluid ; 

 and Mr. Geddes, therefore, considers that, where a weak place in the 

 cellulose wall happens to come opposite the intercellular space, a 

 certain amount of water might easily enter the latter from the cell ; 



* Traus. R. Soc. Edinburgh, xxix. (1881) pp. 555-9 (1 pL). 



