ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 335 



become of longer and longer duration, till they became the permanent 

 stages ; and be is inclined to think that the whole genus Surirella 

 may have had its origin from some species of Auricula — following the 

 law of transmutation which is here for the first time formulated. The 

 paper is illustrated by text figures, and is to be continued. 



Pure Cultures of Diatoms.* — 0. Richter has succeeded in isolating 

 and studying two species of diatoms, Nitzschia Paha W. Sm., and 

 Navicula minuscula Grim. He grew them in gelatin and in agar, and 

 gives the details of his results. He finds that diatoms, like Scenede- 

 s unes acutus, have the effect of liquefying gelatin, and that both his 

 species dissolve agar, forming deep grooves into which they sink. The 

 rate of multiplication depends on the species and the medium em- 

 ployed for cultivation. Strong sunlight injures the cultures, bleaching 

 them and sometimes destroying them. Agar has a marked effect on the 

 form of the diatom, altering according to the strength of the medium. 

 The diatoms showed themselves to be phototactic. As regards nutrition, 

 it was seen that magnesium is absolutely necessary for the diatoms, 1 ut 

 it is probable that Nitzschia PaUa does not require calcium. 



Sphacelariaceae.f — C. Sauvageau has issued a reprint of his 4 Remarks 

 on the Sphacelariacege,' so far as they have already been published in 

 the Journal de Botanique. The remainder of his work will continue to 

 appear in parts in the same Journal. After a short introduction, the 

 author gives an interesting chapter on what he terms Generalities. The 

 general structure of the plants of the order is described, and references 

 are made to the work of Geyler and Magnus ; the conclusions of the 

 latter with regard to the sympodial branching of Sphacelariaceai, though 

 ignored or disbelieved for so long, are shown by Sauvageau to be correct. 

 As regards the relationship between Sphacelariacea? and Ectocarpacese, 

 the author recognises, of course, that such exists, but he points out 

 certain characteristics peculiar to Sphacelariacese only. One of these is 

 the black or black-green coloration of the thallus by eau-de-Javelle. 

 The reacting substance in the cells is as yet unknown. Other characters 

 not shared by Ectocarpacese are the presence of chromatophores in discs 

 or in grains, never in plates or in ribbons ; the almost constant presence 

 of tannin ; and the endogenous growth of the hairs, solitary, in pairs, 

 or in a tuft. The plurilocular sporangia of Sphacelariaceae show an 

 independent dehiscence for each loculus, lout the dehiscence is generally 

 simultaneous. It takes place by means of a dissolution of the wall, 

 and not by tearing. A possible exception to this mode of procedure is 

 Sphacelaria olivacea. A description is given of the antheridia of the 

 order, about which bodies there had been much doubt and discussion. 

 The author has not yet, however, seen copulation nor a fixed zoospore 

 with two red spots. The male nature of the plurilocular sporangia with 

 small loculi is established, but the nature of the other plurilocular 

 sporangia still remains doubtful ; and the author is inclined to think 

 that a study of those genera usually supposed to have no propagula, 



* Ber. Deutsch. Bot. Ges., xxi. (1903) pp. 493-506 (1 double pi.). 

 t Journ. de Bot , xiv., xv., xvi., xvii., 1900, 1901, 1902, 1903, sep. copy, 320 pp., 

 62 figs, in text. 



2 A 2 



