306 I SUMMARY OF CURRENT RESEARCHES RELATING TO 



i 



"Fucosan.* — B. Hansteen gives further arguments that the substance 

 found in brown sea-weeds, and named by him fucosan, is a carbohydrate, 

 the first product of assimilation, and not, as alleged by Crato,f an inde- 

 pendent organism of the nature of a physode. He asserts that it is- 

 readily soluble in fresh water. In Ectocarpus siliculosus he has observed 

 that the fucosan granules are formed within the phaeoplasts, from which 

 they escape, attach themselves to their surface, and then pass into the 

 cell-cavity. Schmitz's " phaeophycese-starch " is simply a young condi- 

 tion of fucosan. "When light is excluded no fucosan is formed (in 

 Sphacelaria cirrhosa). The fucosan granules have no amoeboid motion, 

 as stated by Crato ; their changes in form are simply due to their semi- 

 fluid consistency. 



Chambers and Pores in the Cell-wall of Diatoms.J — 0. Miiller 

 recurs to this subject, replying to the objections of F. Schiitt § to some of 

 his previous conclusions, and to his claim of priority in others. With 

 regard to the size of the pores, he regards the minimum diameter as 

 certainly higher than * 1 /*, the maximum diameter as probably about 

 • 4-0 ' 5 p ; structures whose diameter exceeds • 6 /j. are probably not 

 pores but poroids. The occurrence of true pores in the cell-wall of 

 diatoms is thus considerably limited. It is essentially connected with 

 the centrifugal thickening of the cell-wall by extra-cellular proto- 

 plasm. 



Gelatinous Membrane of Diatoms. || — In two plankton diatoms, 

 Asterionella gracillima and Tabellaria fenestrata var. asterionelloides, 

 M. Voigt finds a gelatinous membrane stretched between the frustules 

 of a colony, which obviously assists the floating capacity of the diatoms. 

 In addition to the membrane, a number of very fine threads, consisting 

 mainly of distinct or closely- packed granules, and often anastomosing, 

 connect the rays with one another. These threads take up carbolfuchsin 

 very strongly, while the membrane itself is but slightly stained. The 

 threads are of protoplasmic composition, and the membrane is apparently 

 excreted from them. 



The author compares the gelatinous membrane with that of the 

 Foraminifera, Eadiolaria, and Heliozoa. 



Colourless Diatoms. H — W. Benecke has investigated the structure 

 and development of two colourless diatoms which are abundant in Kiel 

 harbour, Nitzschia lencosigma and N. putrida (= Synedra pulrida Cohn). 

 With the exception of the complete absence of diatomin, their contents 

 present no peculiarity ; nor is there anything peculiar in their motility 

 or other vital phenomena. Both are small extremely motile forms ; no 

 formation of auxospores could be detected. There appear to be no 

 transitional forms between the brown and the colourless. The latter 

 occur especially in places where there is abundance of decaying organic 

 matter, and their mode of life is obviously saprophytic. 



* Pringsheim'B Jahrb. f. wiss. Bot., xxxv. (1900) pp. 611-25 (1 pi.). Cf. this 

 Journal, 1893, p. 218. f Cf. this Journal, 1893, p. 763. 



% Ber. Deutech. Bot. GeB., xviii. (1901) pp. 480-97 (1 fig.). Cf. this Journal, 

 1900, p. 360. § Cf. this Journal, 1900, p. 613. 



|| Biol. Centralbl., xxi. (1901) pp. 36-9 (1 fig.). 



\ PringBheim's Jabrb. f. wisa. Bot., xxxv. (1900) pp. 535-72 (1 pi.). 



