ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 
75 
and the limit of development is produced by the salt which exercises the 
strongest osmotic power. The results obtained show that with a com- 
bination of salts the reactions are not so simple as might be imagined 
at first. Details are given of the experiments carried out and the 
methods employed. E. S. Gepp. 
Serological Studies with Unicellular Algae. — R. Lieske (Sitz. 
ber. Heidelberg ATcad. Wiss. 1916, B. 3, 48 pp., 4 figs, in text ; see also 
Bot. CentralbL, 1919, 140, p. 135). The cultivation of fifteen species 
of unicellular algae on six different media, organic and inorganic, is 
described, absolute purity being indispensable. The animals into which 
these were injected were rabbit and frog. Methods and results are fully 
set forth. The author finds that the colourless mutations of the algas 
react serologically in the same way as the corresponding green cultures 
grown purely heterotrophically. The serological difference between 
green and colourless cultures is not caused by the presence or absence of 
chlorophyll, but by the autotrophic or heterotrophic method of nutrition 
conditional thereon. From the systematic standpoint it is noted that a 
close albumen relationship exists between Chlorella vulgaris and Sticho- 
coccus bacillaris. The latter belongs, therefore, not to Ulotrichales but 
to Scenedesmacege. E. S. G. 
Coloration of Fresh-water by Plant Life. — E. Naumann (Bot. 
Notiser, 1919,225-339 ; see also Hedwigia, Beiblatt , 1921, 62, p. (88). 
A continuation, (viii) A coloration caused by Scenedesmus quadricauda 
was observed throughout the entire waters of the “ Great Restaurant 
Pond” in the Berlin Zoological Gardens, (ix) A new case of colora- 
tion by Trachelomonetum volvocina var. subglobosa occurred in a pond, 
Plydammen near Ljungby, on very poor heathland, in which the fish 
had been plentifully fed with meal. The author concludes that the 
easily oxidised iron compounds arising from the mud strata represent a 
sine qua non for the development of the Trachelomonas. (x) Scenedesmus 
quadricauda forms a constituent of the coloured mass-production of 
summer plankton in “ Baltic ” lakes. The Falkenhagen lake in 
Brandenburg, not far from Berlin, is cited as having been coloured 
green by this alga in the summer of 1915. It was accompanied by 
numerous colonies of Microcystis , which may perhaps have added to 
the effect, (xi) A feeble coloration by Dinobryon cylindricum was 
observed in July 1915 in the Iguanodon pond in the Berlin Zoological 
Garden. E. S. G. 
Cytological Studies in the Protococcales. ' III. Cell Structure and 
Autospore Formation in Tetresdron minimum (A. Br.) Hansg. — 
Gilbert Morgan Smith ( Annals of Botany, 1918, 32, 459-64, 1 ph). 
Little is known concerning the cytological structure of members of 
Tetrsedron. The author’s investigations show that young cells of 
T. minimum contain a single nucleus and pyrenoid. Repeated 
simultaneous karyokineses may produce as many as eight nuclei within 
a single cell. Autospores are formed by progressive cleavage, the 
number of nuclei increasing during the process. Four, eight, sixteen or 
thirty-two uninucleate protoplasts are the final product of this cleavage, 
