200 SUMMARY OF CURRENT RESEARCHES RELATING TO 



by a successive association (formation ?) of Cladophora, Spiroggra and 

 abundant Diatoms, both free-living and epiphytic, while the principal 

 subsidiary forms are (Edogonium, Mougeotia, and Cyanophyceae. The 

 algal flora shows a well-marked periodicity. Four phases are distinguish- 

 able in a normal annual cycle : (1) Winter-phase with an abundance of 

 free Diatoms ; (2) Spring-phase with dominant Spiroggra ; (3) Summer- 

 phase with dominant Cladophora and abundant epiphytes ; (4) Autumn- 

 phase, chiefly characterised by renewed activity after the inactive summer 

 period, often with a prominent development of Spiroggra, (Edogonium. 

 or some other form. The reproductive processes in the pond show con- 

 siderable uniformitv, which is ascribed to the rather narrow range of 

 temperature in the water. The epiphytic algal vegetation finds its chief 

 host in Cladophora, and one of the most salient features in the annual 

 cycle is the struggle between Cladophora and its epiphytes. The factors 

 operating in the pond are of three kinds, seasonal, irregular, and corre- 

 lated ; these are discussed. Finally, the authors state that all their 

 observations tend to indicate that the doctrine of limiting factors will 

 probably be found to underlie the whole scheme of intricate changes 

 that are so striking a feature of fresh-water algal vegetation. 



Supplement to Engler's Pflanzenfamilien.*— N. Wille publishes a 

 supplement to the volume of Chlorophyceae in Engler's Natiirlichen 

 Pflanzenfamilien, which appeared about twenty years ago. In that time 

 much work has been done on the group, and the author embodies it in 

 the present supplement. In a preface he explains that he does not see 

 his way to recognise the new groups of Heterokontae and Akontae, since 

 the characters which distinguish them are found in the most different 

 and widely separated sections of the green algae ; hence he regards the 

 groups as unnatural. He adheres to the old divisions of Conjugate, 

 Protococcales, and Chaetophorales ( = Confervales). Siphoneae is divided 

 into two sections of equal value, Siphonocladiales and Siphonales. In 

 the former section are placed, besides Yaloniaceas and Dasycladaceas, 

 the families Oladophoraceae and Sphaeropleaceas. Another addition 

 to the treatment of the Chlorophyceae is the inclusion of a series of 

 colourless organisms, hitherto reckoned with the fungi, and now re- 

 garded as akin to Yolvocaceas, Plcurococcaceae, Oocystaceae, and (Edo- 

 goniaceae. 



Indian Ocean Plankton.f — F. Czapek gives a short account of plank- 

 ton material which he collected in the neighbourhood of Karachi. He 

 found it to consist entirely of diatoms, of which he enumerates twenty- 

 eight species. Many of them have been already recorded in the plankton 

 of the Gulf of Aden. The author then discusses the phosphorescent 

 Peridinieae of the Indian Ocean, and gives a list of eleven species, col- 

 lected by himself, which produced phosphorescence. The species which 

 takes the greatest part in this phenomenon is Ceratium tripos. Figures 

 are given of stages of division in Coscinodiscus sgmmetricus, as well as of 

 a Dinopligsis which was continually found connected in pairs. Other 

 stages of division were, however, not found in the latter species. 



* Die Natiirlichen Pflanzen., Suppl. to Teil. i., 2te Abt. (1909) 9G pp. (figs, in text), 

 t SB. k. Akad. wiss. Wien, cxviii. (1909) pp. 231-9 (5 figs.). 



