ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
419 
depends. Possibly, as Hjort suggests, the survival of large numbers of 
newly hatched food-fishes in early spring is determined by the amount 
of phytoplankton present, and thus is ensured or destroyed the prosperity 
of commercial fisheries a few years later. The vernal increase in phyto- 
plankton seems to depend upon the rapid increase in the solar energy 
during the lengthening days of early spring. The diatom maximum in 
spring is doubtless aided by the winter increase of carbon dioxide and 
other food-matters in the sea, and the rapid disappearance of diatoms 
after the maximum may be due to some toxic effect upon the water 
caused by their own metabolism in dense crowds. Numerical conclu- 
sions cannot be with safety drawn from few and small samples of the 
plankton. Even when taken in rapid succession the hauls show great 
variation. The distribution of plankton is not uniform but in patches. 
A. Gepp. 
Study of Some of the Factors Controlling the Periodicity of 
Fresh-water Algae in Nature. — William J. Hodgetts ( New Phyto- 
logisi, 1921, 20 , 150-64, 11 figs. ; 195-227, 6 figs. ; 1922, 21 , 15-33, 
2 figs.). An account of observations of the algal flora of a small pond 
near Birmingham from January 1918 to June 1921. It is presented 
under the following headings : — 1. Introduction. 2. General account 
of Hawkesley Hall Pond and its phanerogamic flora. 3. Meteorological 
data. 4. Concentration of the water. 5. Algal flora of the pond 
— three groups : common, moderate, rare. 6. General account 
of the annual cycle of the predominant algal species. 7. Spirogyra. 
8. Zygnema and Mougeotia. 9. Desmidiacese. 10. Oedogoniacese. 
11. Tribonema. 12. Microspora. 13. Vaucheria. 14. Aphanochsete 
and Draparnaldia. 15. Nitella and Coleochsete Nitellarum. 16. Proto- 
coccales. 17. Yolvocales. 18. Cyanophyceae. 19. Flagellatae. 20. 
General conclusions regarding the concentration of thew T ater. 21. Sum- 
mary of the chief results. A bibliography is appended. A. G. 
Life-history of Staurastrum Dickiei. — Charles Turner (Journ. 
of BoL, 1922, 60 , 189-90). An account of the effect of the drought 
of 1921 upon the desmid Staurastrum Dickiei var. parallelum, resulting 
in the production of a great number of zygospores in mountain pools 
in Denbighshire. The spore contents were at first of an oily nature, 
obscuring the view of the nucleus ; but at a later stage the production 
of four nuclei was readily visible, an indication apparently of a diploid 
nucleus after conjugation, followed by a reduction division within the 
zygospore. The germination of the spore results in the formation of 
four, three, two or one desmid only, accompanied by an atrophy of some 
of the “ mother cells.” The process of conjugation is usually normal ; 
a conjugation tube is rarely observed. The conjugating desmids are 
asymmetrically placed. The conjugation of a 4-rayed with a 3-rayed 
form was not infrequent ; and both forms were seen in the protoplasm 
discharged from the same spore on germination. Vegetative propaga- 
tion was often accomplished by the development of a single spherical 
bulging cell between the two semi-cells ; and the contents of this might 
divide, or an hour-glass constriction might cause ultimate formation of 
two desmids. A. G. 
