62 SUMMARY OF CURRENT RESEARCHES RELATING TO 



generally on damp rocks and stones. It forms a thin mucous stratum 

 of a dark green colour, which, when dry, becomes almost black and 

 peels off the stone. The stratum consists of large numbers of thin- 

 walled cells imbedded in a colourless mucilage. These cells are, for the 

 most part, somewhat irregularly or obliquely ellipsoid. Multiplication 

 takes place by oblique fission, the mother-cell dividing into two, or 

 occasionally four, daughter-cells. Reproduction takes place by the 

 formation of four, rarely eight, non- motile gonidia, and also by 

 the formatiou of macro- and micro-zoogonidia, 2, 4, 8, and 16. The 

 cultures of the alga, grown by the author, are described, as well as 

 her observation of the formation of zoogonidio. As regards the 

 systematic characters of C. subellipsoidea, it differs from C. dispar 

 Schmidle, in the greater regularity in the form of the cells and in the 

 presence of pyrenoids. It shows a great resemblance to Oocystis 

 submarina Lag., in the oblique division, and in the form of the cell 

 and of the chloroplast. 



Sphserella lacustris.* — F. Peebles describes the life-history of 

 Sphserella lacustris, with special reference to the nature and behaviour 

 of the zoospores. The cycle of development is discussed and the 

 author's views compared with those of other authors. The results are 

 summarised as follows: — 1. Normal resting-cells from wild cultures 

 always produce asexual zoospores by endogenous division. These 

 spores swim about for a short time, gradually becoming larger, and 

 finally assuming the typical pear-shape with distended cell-wall, long 

 flagella, and protoplasmic threads between the wall and the central mass. 

 2. The zoospores divide, either while swimming about or after a short 

 period of quiescence, forming several generations of motile spores. 

 Multiplication is by endogenons cell-division, and in rare cases by 

 fission. 3. After a number of generations have been produced, the 

 cells settle down for a period of rest and growth. Many of them attain 

 great size, and finally divide into 16 to o2 non-motile cells, which, in 

 turn, grow into large resting-cells. They divide in the usual way, 

 forming a new generation of zoospores. 4. Resting-cells, which have 

 been subjected to adverse conditions, such as starvation, cold, rapid 

 drying, or a very brief rest, usually produce small motile spores of 

 gametes. 5. By conjugation two gametes form a zygospore. This 

 zygospore remains active for a few hours, then settles down, secretes a 

 wall about itself, losing its four flagella. After a period of growth and 

 rest, the zygospore continues the cycle of development by dividing to 

 form the asexual zoospores. Finally the author suggests that since the 

 megazoids are known to be asexual and the microzoids sexual, they 

 should be termed respectively zoospores and gametes. 



Scenedesmus-t— Schmula describes a new species of Scenedesmus, 

 S. jproductocapitatus, which was found in a ditch near Oppeln. Speci- 

 mens are to be distributed on talc, as No. 728 of the Phykotheka 

 Universalis. Nine other species of fresh-water alga? are enumerated, 

 which were found at the same place. 



* Centralbl. Bakt. Parasitenk., 2te Abt., xxiv. (1909) pp. 511-21 (figs.), 

 t Hedwigia, xlix. (1909) pp. 85-7 (figs, in text). 



& 



