ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 415 



favourable character have been made in the simultaneous extraction of 

 iodine and of tangates. The proportion of tangates and the metabolism 

 of iodine are at present in course of investigation. E. S. G-. 



Fucosan Bladders of the PhseophyceEe. — H. Kylin {Ber. Dentscli. 

 Bot. Ges., 1918, 36, 10-19; see also Bot. GentralbL, 1919, 140, 120), 

 After a review of past work on the subject by other writers and by 

 himself, the author emphasizes his own view that the substance in 

 question is related to tannin. It is not a first product of assimilation, 

 such as carbohydrate, but is probably an insignificant bye-product. It 

 has no connexion with Laminarin. The Fucosan bladders are said to 

 facilitate the escape of assimilation products from the chromatophores. 



E. S. G. 



Temperature Interval in the Geographical Distribution of 

 Marine Algae.— W. A. Setchell (Science, N.S., 1920, 52, 187-90). 

 A short preliminary account of the work described in stenothermy and 

 zone-invasion (see below). An instance is given of sharp division in 

 the distribution between the northern and southern species. At the 

 entrance to Vineyard Sound the surface temperatures in the summer 

 are slightly above, and the bottom temperatures are slightly below 

 20° C. ; and the southern species are found in the surface waters, while 

 the northern ones inhabit the depths. The isotherms, both isotheres 

 and isochrymes, of 10°, 15°, 20°, and 25° C. definitely limit the exten- 

 sion of particular floras of marine alga3. The author suggests possible 

 lines of research for determining the explanation, such as the varying 

 viscosities of the sea water, or its power to dissolve gases such as oxygen 

 or carbon dioxide ; or again, the activities of some particular enzyme 

 or group of enzymes which act effectively only within narrow limits of 

 temperature. E. S. G. 



Stenothermy and Zone-invasion. — W. A. Setchell {American 

 Naturalist, 1920, 54, 3N5-97). An account of further investigations 

 by the author on the zonal distribution of marine algse. After a brief 

 summary of the work of former botanists, and of the papers by himself 

 on this subject, the author discusses the distribution of algse on the 

 coast of New England. He finds that the species may be readily 

 arranged in two categories — one, of the colder waters (20° C. or less), 

 and the other of the warmer waters (20° C. or over) ; and while some 

 species are found only north of Cape Cod and others only south of it, 

 the majority are found on both sides of the Cape, which is the natural 

 dividing point, and approximates closely to the position of the 20° C. 

 isothere. The temperatures for normal persistence of any particular 

 species of marine plant lie within narrow limits, and the favourable 

 interval is very little, if any, over 10° C. This leads to a discussion of 

 the terms " stenothermal " and " eurythermal " hitherto used mostly by 

 zoologists — the former indicating species having a limited range, the 

 latter a wide range. Eurythermal species are : Ascophyllum nodosum, 

 Rhodocorton Rothii, Monostroma GreviUei, Polysiplionia urceolata, and 

 Grinnellia americana. Stenothermal species are particularly character- 

 istic of the Tropical zone. The nature of the fundamental differences 

 between the eurythermal and the stenothermal species are considered 



