326 THE JOURNAL OF BOTANY 



and figured by Hustedt''^ in Eunotia hinaris, although again there 

 is no evidence that these were resting-spores. 



On the date mentioned the temperature of the water in the 

 bog, which is fed by a spring, was 3-6° C. 



XII. — A New Genus of Yolvocace^. 



Early in the March of this year, Mr. D. J. Scourfield, of 

 Leytonstone, sent me a tube containing large numbers of living 

 specimens of a minute member of the Chlamydomonadeae. This 

 organism, which is one of the smallest of the Yolvocaceas, has 

 proved of very great interest, and the following genus is proposed 

 for its reception : — 



Scourfieldia, gen. nov. CeUulse vegetativae minutissimae, 

 libere natantes et motiles, valde comp-essce, ; a fronte visae pler- 

 umque late elliptico-ovatae vel nonnunquam ellipticae, polo uno 

 cum incisura minuta et cilios binos perlongos praedito, altero 

 rotundato ; a latere visae anguste oblongge, lateribus subparallelis 

 et polls rotundatis. Chromatophora singula, viride, subcampanu- 

 lata sed compressa, sine pyrenoide ; nucleo singulo ; stigma carente. 

 Propagatio ignota. 



S. complanata, sp. nov. (Fig. 3.) Long. ceU. 0-2-5-7 fx; 

 lat. cell. 4-4-4-6 /x; crass. 1-8 fx; long, ciliorum 18-5-20 /x. 



Hab. In pond on Leyton Flats, Essex {D, J. Scourfield ; 

 Jan.-April, 1912). 



Mr. Scourfield writes that this minute organism " occurred in 

 myriads, the water of the pond being distinctly green without 

 any noticeable alteration in intensity from about the middle of 

 January to the middle of April, 1912. This period included one 

 week of severe frost when the pond was covered with fairly thick 

 ice. The green colour of the water was due entirely to this one 

 organism." 



The cells vary in shape very slightly, but are for the most part 

 ovate-elliptic, and the cilia are attached to the base of a minute 

 notch at the narrower pole. The outstanding features of the 

 organism are first, the great compression of the cell ; and secondly, 

 the great length of the cilia, which are relatively longer than those 

 of any other member of the Volvocacege. The chloroplast is rather 

 thin and bell-shaped, enclosing within its central hollow a rather 

 large amount of the colourless protoplast. There is no pyrenoid, 

 and iodine solution failed to reveal any particles of starch in the 

 specimens examined ; in fact, the chloroplast appeared absolutely 

 homogeneous. The nucleus is almost central in position, and in 

 specimens treated with iodine there is a small clear space between 

 the nucleus and the base of the cilia, rather to one side of the 

 median line, which probably represents the position of either one 

 or two contractile vacuoles (fig. 3, Av). Between the nucleus and 

 the thick posterior part of the chloroplast are two or three minute 



* F. Hustedt, "Beitrage zur Algenflora von Bremen. IV. — Bacillariaceen 

 aus der Wumme," Abb. Nat. Ver. Bremen, xx. 1911. 



