600 SUMMARY OF CUKKENT RESEARCHES RELATING TO 



develops in it; and a nuclear membrane forms. The metachromatin 

 granules of the cytoplasm disappear. The chromatin of the nucleus 

 aggregates into a large karyosoma. This divides by transverse fission ; 

 so, too, does the cytoplasm ; the halves round off, and daughter-cell walls 

 are formed. 



Glaucocystis probably belongs to the Cyanophyceas, because of the 

 " open " nucleus, the tendency of cytoplasmic division to take place in- 

 dependently of nuclear division, and the presence of phycocyanin in 

 the chromoplast. The very high differentiation of the nucleus in the 

 dividing stage, the elaborate chromoplast to which the phycocyanin is 

 confined, the formation of daughter-cells like those of Oocystis, and the 

 cellulose wall, are features that separate Glaucocystis from all other 

 Cyanophyceas, and probably justify the placing of this genus in a special 

 group of Cyanophycege. 



Pleodorina illinoiensis in Britain.* — W. B. Grove gives a detailed 

 account of the structure, movements and life-history of Pleodorina 

 illinoiensis, an American alga which he collected in quantity in cart-ruts 

 at Harborne near Birmingham, and kept under observation. He com- 

 pares it with Eudorina and Pandorina, and finds the distinction drawn 

 between Eudorina and Pleodorina to be a somewhat slender one, so far 

 as it relates to the difference in shape of the colonies and in size among 

 the cells in the same colony. Pleodorina is an advance on Eudorina in 

 the direction of Volvox, where the distinction between somatic and 

 reproductive cells is strongly accentuated. 



Plankton of the Mansfeld Lake.f — F. V. Coditz writes on the 

 biology of the Mansfeld Lake with special reference to the centrifugal 

 plankton and its relation to the net-plankton of the pelagic zone. The 

 lake lies in Saxony and is the largest inland water of Middle Germany. 

 It was formerly an old river valley. The water is a dirty -green to brown 

 colour. The centrifugalized alga? show a small number of species in 

 consequence of the salinity, but the number of individuals is enormous. 

 In spring the principal food of the net-plankton consists of the develop- 

 mental stages of Microcystis aeruginosa Lernrn., which were demonstrated 

 for the first time by means of the centrifugal apparatus. Microcystis is 

 developed pelagically. The maximum of the centrifugal plankton fell 

 during the spring and autumn circulation of the water. Widely spread- 

 ing out forms or those with a gelatinous sheath are of no use for food 

 for animal plankton. The water-bloom is encouraged by slightly salt 

 water. The phyto-plankton of this lake differs from that of the hitherto 

 known types of the larger North German waters by the lack of the 

 dominating BacillarieaB, Melosira, Fragilaria, Asterionella, as well as 

 Dinobryon, Ceratium and Peridinium. Botryococcus Braunii is present 

 in spring and autumn plankton. Finally, the author discusses the 

 relations between centrifugal and net-plankton. 



* New Phytologist, xiv. (1915) pp. 169-82 (figs.). 



t Zeitschr. wiss. Zool., c. (1914) pp. 520-630. See also Bot. Ceutralbl., cxxix. 

 (1915) p. 250. 



