ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 483 



pass over into the latter, which are much more rare than would appear 

 at first sight. The true nature of the branches reveals itself for 

 the most part only in the earliest stages of their evolution. The 

 flagella which result from them consist of a single filament of cells or, 

 at the base, two rows of united cells, neither of which must be considered 

 as an abortive branch. 



Sexuality of Spirogyra.* — B. Cunningham discusses the question of 

 sexuality in Spirogyra, and comes to the following conclusions : 

 1. Bisexuality of the filament does occur in certain species of Spirogyra, 

 but not necessarily in all species. 2. Reduction may occur in the zygote, 

 in which case a filament wholly of one sex arises, or reduction may occur 

 just previous to reproduction, in which case none of the nuclei 

 degenerates, and filaments of a bisexual nature are produced, which 

 would conjugate either laterally or by cross-conjugation. 3. Cell- 

 division may take place subsequent to reduction, some cases showing- 

 three divisions, and this is an essential difference between lateral and 

 cross-conjugation, since the latter may continue cell-division after 

 reduction is complete, but the former apparently does not. 4. The filament 

 of Spirogyra, in the species examined and in those with lateral conjuga- 

 tion, is homologous with the sporophyte of higher plants. The species 

 examined showed some of the characteristics of S. inflata, but differed 

 from it in certain particulars. It may therefore be a new species. 



Dictyosiphon foeniculaceus.t — C. Sauvageau writes on a new type 

 of alternation of generations in Brown AlgEe, as exemplified by 

 Dictyosiphon famiculaceus. More than forty years ago Areschoug 

 described a conjugation between germinations of zoospores in D. 

 Iiippuroideii, but his work has never been either confirmed or 

 contradicted. The material of D. fceniculaceus for the present research 

 was sent by M. Corbiere from Cherbourg to the author in September 1916, 

 and he then started some cultures. Some of the filaments fruited after 

 more than five months of culture, at the end of February, and these 

 were the gametophyte of Dictyosiphon. Dehiscence takes place at all 

 hours of the day. The zoospores, about 7 ^ by 4 /a, having a single 

 chromatophore and a red spot at the insertion of the cilia, become fixed 

 on the side opposite to the window, and round themselves off with a 

 diameter of about 4 • 5-5 /a. The germiuation of the embryospores is 

 general and almost immediate. Twenty-four hours later a creeping 

 tube is produced, one to three times as long as the diameter, and 2 fx. 

 wide. This prothallus elongates rapidly ; after three days it has already 

 one or two cross-walls. At no period does conjugation take place, as 

 described by Areschoug. Three weeks later the prothallus measures 

 l()0-:3()0 /A, and it has emitted here and there creeping branches in 

 various directions. Some of its cells are long and slender, others are 

 short and stumpy. The embryospore remains distinct, or enlarges and 

 produces a branch. Growth and ramification continue, and towards the 

 fifth week there appear long sessile colourless hairs, 3-4 /u, wide. The 



* Bob. Gaz., Isiii. (1917) pp. 486-500 (3 pis.). 

 t Comptes Rendus, clxiv. (1917) pp. 829-31. 



2 K 2 



