ZOOLOGY A.ND BOTANY, MICROSCOPY, ETC. 633 



The first class is divided into two types. I. An auxospore formed 

 of a single mother-cell (in this division there is one sub-type). II. Two 

 auxospores formed from a single mother-cell (here there are two sub- 

 types). 



The second class contains three types : III. Two mother-cells divide 

 into two sister-cells, each half copulating with the half of the other 

 individual and forming an auxospore. 



IV. Two cells form an auxospore (there is a sub-type here to contain 

 Cocconeis). V. Two cells come into contact but do not copulate, pro- 

 ducing two auxospores, — reduced sexuality. 



Details are given concerning the behaviour of the nucleus and 

 nucleolus in these various types, as well as explanatory figures and 

 diagrams. Finally, genealogical trees showing the views of the author 

 and those of Karsten concerning the evolution of diatoms, place the 

 divergence of views clearly before the reader, and the respective arguments 

 are set forth in the text. 



Endochrome of Diatoms.* — C. Mereschkowsky publishes the first 

 part of his studies on this subject and treats therein more especially 

 of facts concerning the Kaphidieae and the Nitzschieae. A more or less 

 detailed account is given of the interior structure of 125 species and 

 varieties of 19 genera belonging to these groups. As regards the 

 endochrome of the family Pleurosigniere, the author finds that Cleve's 

 distinction between Pleurosigma and Gyrosigma is quite correct, Pleuro- 

 sigma possessing four tortuous bands, and Gyrosigma two (in the case of 

 G. rectum four) plates. The division of diatoms into Coccochromea? and 

 Placochromeas should, according to the author, be definitely abandoned, 

 as being without sound foundation. The study of the endochrome 

 as a generic character has little value, but as a specific character it 

 is of the deepest importance. The " primary " elaeoplasts, as distin- 

 guished from the " secondary " or " supplementary " ones, are also 

 shown to be constant in form, and therefore of value in systematic 

 determination. The paper is well illustrated. 



Melosira. | — 0. Muller discusses the occurrence of a possible variation 

 without intermediate stages, in certain species of Melosira. He has 

 found threads which are composed of individual diatoms having pores 

 of large size and others with pores of small size, and some threads com- 

 posed of both kinds. All three kinds of threads are perfectly distinct in 

 appearance. The specimens examined and compared come from the 

 Lake of Nyassa and the Muggel-See, near Berlin. He regards the 

 coarse-pored Muggel-See plant as Melosira granulate Ealfs, and makes 

 two sub-species : 31. mutabilis with joints snowing both sizes of pore, 

 and 31. punctata, with fine round pores. - The coarse-pored species from 

 Lake Nyassa he calls 31. Nyassensis, and this is also divided into two 

 sub-species : 31. cle Vriesii with mixed pores, and 31. bacillosa with fine 

 rod-like pores. The diagnoses are promised in a later paper in Engler's 

 Jahrbuch. The author refuses to recognise 31. crenulata var. ambigua 



* Mem. Acad. Imp. Sci. St. Petersbourg, ser. 8, xi. No. 6 (1901) 140 pp., 7 pis. 

 (fig-, in text). 



t Ber. Deutsch. Bot. Ges., xxi. (1903) pp. 326-33 (1 pi.). 



