ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 375 



species out of the total of 444 recorded ; in South Georgia, 42 endemic 

 out of 93 ; in Antarctica, 24 out of 47. He shows conclusively that the 

 Magellanic moss-flora has closer affinity to that of Australasia than to 

 that of Patagonia, the former land connection being probably indicated 

 by the islands of Falkland, South Georgia, Kerguelen, Auckland, and 

 New Zealand. On the Antarctic continent itself a slow immigration 

 and adaptation of species has been going on. 



Thallophyta. 



Algae. 

 (By Mrs. E. S. Gepp.) 



Bisection of a Monad by a Diatom.* — P. A. Dangeard publishes 

 a note on an instance of accidental bisection performed by a Navicula 

 upon the minute unicellular organism Chrysomonas Jiavicans Stein. The 

 Navicula acted like a knife, and by its own motive power pushed its 

 way through the Chrysomonas and divided it into two portions, which 

 after ten seconds came together and united again, the cell soon regaining 

 its normal form and independent life. The author adds the following 

 reflections: — 1. The protoplasm of Chrysomonas is evidently very 

 fluid, its particles having very feeble cohesion. The degree of cohesion 

 might be actually measured by utilising this movement of the Navicular 

 against droplets of substances having a known density and resistance. 

 2. We are still ignorant of the nature of the movements of diatoms. 

 The theory that they move by excreting a gelatinous secretion from 

 their posterior end is open to great doubt : for in the present case the 

 secretion must at once have become of a higher consistence than that 

 of the protoplasm of Chrysomonas. 3. The reunion of the two 

 portions of the Chrysomonas shows the persistence of an attraction 

 between the separated halves of a cell. AVhat prevents two cells of the 

 same species from uniting ? There is an unknown law to be discovered 

 here. 



Periodicity in Spirogyra.f — W. F. Copeland has been studying the 

 question of periodicity in Spirogyra during the past few 7 years. He 

 started some hundreds of aquaria, and found the best way to arrange a 

 culture was to place sterilised earth in the bottom, add dead leaves or 

 dead grass, and, after allowing all to settle down in the water, to add a 

 small amount of Spirogyra, and place at first in a window not exposed to 

 direct sunlight. The time of fruiting of any given species coincided 

 with the time of fruiting in the wild state. Five p.c. of the cul- 

 tivated material fruited. Of the thirteen species under cultivation 

 twelve formed fruit ; the other species, though kept under observa- 

 tion indoors and out since October 1905, has remained sterile. Ten 

 of the species were at their maximum abundance in May, one in 

 August, one in October. Secondary fruiting in July occurred in 

 S. dubia. For the examination of wild specimens it was found to 

 be expedient to carry the microscope into the field. Maximum abun- 

 dance coincides in every case with maximum conjugation. After 



* Bull. Soc. Bot. France, lv. (1908) pp. 641-3- 

 t Bot. Gaz., xlvii. (1909) pp. 9-25. 



