ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 579 



cultures of the algge studied are not sufficient to warrant any assumption 

 of widespread polymorphism among the algae. 



Protection of Fresh-water Algae against Animals.* — H. Michaelis 

 publishes the result of his investigations into the methods adopted by 

 fresh- water algge to protect themselves from being eaten by animals. 

 The result is achieved sometimes by chemical substances, or by external 

 development, or by a covering of slime or jelly. The efficacy of 

 chemical means was proved by removing the protective substance from 

 an alsra and offering it to water-animals together with fresh material. 

 They chose the former. Experiments with various chemical substances 

 ai'e described. Ckromtilina Rosanoffii is protected by the fact that its 

 resting cells on the surface of the water are out of the reach of 

 microscopical and semi-microscopical crustaceans ; and Chromulina is 

 therefore able to multiply and make good the damage done by devouring 

 animals. The author has also investigated the effect of incrustration 

 on algte. In some cases incrusted algte escape being eaten, but on the 

 other hand diatoms and desmids form a food supply for certain animals, 

 "What may Ije the defensive factor in certain incrusted algge is not 

 known. Bristles and external excrescences are efficacious as a rule, but 

 not entirely so. Instances are given of even Ceratium hinmdinelJa 

 being devoured by animals. The author considers that gelatinous 

 coverings act quite as well as chemical and mechanical methods of 

 protection. 



Fresh-water Algse.t— E. L. Piatt discusses the population of the 

 " blanket-algfe " of fresh-water pools — in other words, the community of 

 life which is found among floating masses of filamentous algfe. The 

 material came from pools at Ithaca, near Cornell University, U.S.A. 

 The most frequent alga was Spirogyra varians, which was largely 

 associated with Mougeotia and Zggnema. A great variety in seasonal 

 conditions was observed. The population inhabiting the masses of 

 filamentous alga3 consisted of diatoms, desmids and other algas, as well 

 as animals. The dominating diatoms were Cocconema, Navicida, 

 Gomphonema, and Synedra. Other algse were best represented by 

 Closteriirm, DictyospJiseriiim, and Dinohryon. The seasonal variation 

 was different in the different pools. 



Nuclear Division in Desmids. | — Elizabeth Acton publishes the 

 first of a series of studies on nuclear division in desmids, and gives an 

 account of what occurs in Hyaloiheca xiissilieiis (Sm.) Breb. Desmids, 

 with few exceptions, do not tolerate artificial conditions, and therefore 

 cannot l)e cultivated with success ; and it is a matter of chance that they 

 should be found undergoing division under natural conditions. Hyalo- 

 theca was obtained in sufficient quantity to yield complete results, but 

 unfortunately its nucleus is too small to show all that is desired. In 



* Jahresb. Grossh. Realschule Schonberg (Meckl.). Schonberg : Lehman und 

 Bernhard (1915) 38 pp. See also Bot. Centralbl., cxxxii. (1916) pp. 137-9. 



t Amer. Nat., 1915, pp. 754-62. See also Bot. Centralbl., cxxxii. (1916) p. 238. 

 X Ann. Bot., xxx. (1916) pp. 379-82 (1 pi. and figs.). 



