74 SUMMARY OF CURRENT RESEARCHES RELATING TO 



form and the posterior protuberances were as marked as ever, yet a 

 greater number of stages transitional between it and Eudorina were 

 found intermixed. And the author claims these as an entire justifi- 

 cation of his suspicion that this Fhodorina is merely a well-marked 

 mutation of Eudorina — on the way to becoming a species. 



Spirogyra.* — S. S. Chien describes the peculiar eiTects of barium, 

 strontium, and cerium on Spirogyra. He summarizes his results as 

 follows : — 1. The chloroplasts of certain species of Spirogyra contract 

 away from the cell-wall in a peculiar and characteristic fashion in 

 solutions of CeCl.^, BaCL, and BrCl., (in the case of the smaller kind 

 in the last two only). The effect is observed in dilutions as great as 

 O • 00005 M of CeClg (in the case of the larger species), and in • 0001 M 

 of BaClo. SrClo also produces this efifect, but not at such great 

 ■dilutions as CeClg and BaCI.,. 2. In the smaller species of Spirogyra 

 the effect of BaCl., is inhibited when BaCU is mixed with CeCla or 

 •CeCla in proper proportions. 



Starch-formation in Zygnema.f — Helen Bourquin has studied the 

 subject of starch-formation in algte, and has chosen Zyg^iema for 

 investigating the process, on account of the large size and the typical 

 nature of its chromatophore. She gives a resume of previous work on 

 the subject, describes her own material and methods, and then gives an 

 account of her work, which she summarizes as follows : — The chroma- 

 tophore of Zygnema is a plastid containing embedded in its substance 

 a pyrenoid which lies near the middle, and starch-grains which usually 

 lie radially about the pyrenoid. The pyrenoid cannot take part in 

 starch-formation because it is always confined to the centre of the 

 plastid and is separated from the starch by the plastid, and because 

 the small young grains of starch are always found in the periphery 

 of the plastid. The plastid, therefore, must form these minute starch- 

 grains. The starch-grains come to lie radially about the pyrenoid in 

 the following manner : — The plastid adds to them in such a way that 

 they become cuneate in sliape. In this manner they grow down 

 between the starch-grains already formed until they are of the same 

 length as the large grains. The plastid then broadens them at the base 

 until they become rectangular in shape. 



Dichotomosiphon tuberosus.:}: — A. de Puymaly writes on Dichotomo- 

 siphon tuberosus, which he lias studied from living material collected by 

 him near Bagneres-de-Bigorre, at a height of about 600 metres. It was 

 growing in a small basin, 10 by 20 metres, in which the water was 

 •continually being renewed and was tepid to the touch, being 20" C. The 

 alga was growing so luxuriantly that it almost covered the bottom of the 

 basin, which was 1 to 2 metres deep. The plant evidently requires 

 warmth, in which it resembles its near allies, the Udotete group. In 

 contrast to Vmicheria, the filaments of D. tuberosus are upright and 



* Bot. Gaz., Ixiii. (1917) pp. 406-9 (figs, in text). 

 t Bot. Gaz., Ixiv. (1917) pp. 426-34 (1 pi.). 

 X Bull. Soc. Bot. Geneve, 1917, pp. 120-5. 



