334 SUMMARY OF CURRENT RESEARCHES RELATING TO 



remarkable feature is the smooth co-operation of the four cells in loco- 

 motion. The author suggests a working hypothesis as to the origin of 

 these groups, the gist of which is that after tlie formation of a zygospore, 

 or auxospore, four bodies are produced within it by division and sub- 

 division, in the manner of Tetraspora. These four final spores, still 

 within a common gelatinous sheath, then shape themselves into four 

 new and full-sized diatoms, and align themselves into a typical group of 

 N. socialis, which then escapes from the confining jelly. 



Zygnema.*— L. Kurssanow gives an account of the fertilization, 

 fruiting, and germination of Zijgnema. His results are as follows : — ■ 

 1. During conjugation the axis of the male protoplast twists itself 90°, 

 in such a way that first the chromatophore, then the nucleus, then the 

 second chromatophore pass through the copulation-canal. The female 

 protoplast remains meanwhile unchanged in its position. 2. In the two 

 species examined, the union of the nuclei follows soon after the conjuga- 

 tion of the gametes, but in Z. stellinum the nuclei generally unite 

 markedly later than in Z. crmiatum. 3. In the ripening zygote the 

 two male chromatophores break up immediately after the formation of 

 all the zygote-walls. 4. The primary nucleus of the zygote thereupon 

 divides twice. The first division of the nucleus is a reduction-division 

 "with the stages of synapsis and diakinesis. The chromosomes develop 

 themselves out of the chromatin-filament of the synapsis in diploid 

 number. In the diakinesis 25-28 chromosomes can be counted. In 

 the prophase they apparently unite in pairs, and there appear fourteen 

 chromosomes (haploid number). The first nuclear spindle is inclined 

 to lie across the axis of the zygote. The second division follows imme- 

 diately after the first, both sister-nuclei dividing simultaneously. The 

 number of the chromosomes of the second division is fourteen from 

 the beginning. 5. Of the four developed secondary nuclei of the zygote, 

 three degenerate, but one grows and assumes the position of the primary 

 nucleus. Conjugation of two secondary nuclei (Chmielewski's second 

 conjugation) does not take place. If by chance two nuclei only de- 

 generate, the other two remain separated up to the end, and this binu- 

 cleate zygote develops a binucleate sporeling. 6. The division of the 

 nuclei in the zygote is atavistic, inherited from the ancestors of the 

 present Zygnemacese, which, like the Mesotffiniacese, have developed four 

 germs in each zygote. 7. The first division in the sporeling is a simple 

 one, allotypic, with fourteen chromosomes ; the second and third di- 

 visions are absolutely identical with the first. 



Extranuclear Chromatin in Vaucheria.t — F. Moreau calls atten- 

 tion to some extranuclear chromatin-bodies in Vaucheria, the significance 

 of which he does not know, but proposes to study. They are permanent, 

 and undergo division. He has found similar bodies in Viola, Arum, 

 Anemone, Equisetum, etc. They are minute, and are frequently situated 

 on the surface of the Chromoleucites. They stain like the nuclei. After 

 division, they remain connected by a fine thread. 



• Flora, n.f., iv. (1911) pp. 65-84 (1 pis.). 

 t Bull. Soc. Bot. France, Iviii. (1911) p. 452. 



