Feeeuaey 12, 1904.] 



SCIENCE. 



261 



The cell membrane consists of chitin with a 

 very small amount of cellulose and pectin. 

 In the heterocysts, however, a layer of cellulose 

 is laid down when it (the heterocyst) begins 

 to develop. In those genera with sheaths the 

 filaments lie free in the sheath except the 

 heterocysts, which are grown fast to it. Kohl 

 sees in this the explanation of the function 

 of these cells. They serve as points of resist- 

 ance in the formation of hormogones, and in 

 the branching of the filament. What the 

 function can be in the forms without a sheath 

 he does not clearly explain. They are evi- 

 dently, however, not reserve cells, for they orig- 

 inate by the formation of stoppers for the pores 

 through which alone the adjacent cells could 

 furnish or receive reserve stuffs. They then 

 build the cellulose wall and totally degenerate. 

 Here and there in the filament a single cell 

 or several cells soften and degenerate, forming 

 the points at which the filament breaks when 

 it divides or produces hormogones. In the 

 forms with false branching such degenerated 

 cells are formed below the heterocysts and 

 seem to help soften the sheath wall so as to 

 enable the filament to turn out through the 

 sheath when the resistance of the fast-grown 

 heterocyst prevents its growing further in a 

 straight line. 



Normally the cells have no cell-sap vaciioles. 

 They resemble meristematie cells in the size 

 of the nucleus and density of the cytoplasm. 

 Only in old or terminal cells and in the hetero- 

 cysts do such vacuoles occur. The so-called gas 

 vacuoles that Kohl mentions as occurring in 

 some Cyanophyceas have been proved definitely 

 by Molisch and Brand, working independently, 

 to be not of gas nature. 



All cells are connected by a fine thread of 

 plasm, which penetrates the center of the pore 

 in the cell wall; even in the heterocysts where 

 the pore is filled up the plasma thread remains, 

 but it is unable to convey enough foodstuffs to 

 keep the heterocyst plasma in good condition. 



The nuclear division was made the object of 

 especial study. By staining the living cells 

 with methylene-blvie Kohl was able to follow 

 the process without subjecting himself to the 

 criticism that his chromosomes were artefacts. 

 The nucleus consists of a ground mass and a 



difiicultly visible fine chromatin-bearing fila- 

 ment. This thickens itself and finally forms 

 a spirem. This breaks up into usually six 

 straight chromosomes which arrange them- 

 selves parallel to the long axis of the thread. 

 They then begin to bow in somewhat, until 

 they are much farther apart terminally than 

 centrally. They then divide crosswise in the 

 middle, not lengthwise, and collect at each 

 end of the cell. At this point in the division 

 a few achromatic fibers are visible, connecting 

 the two masses of chromosomes, but no spindle 

 in the proper sense is seen. The daughter 

 chromosomes arrange themselves parallel, then 

 form a spirem. As the chromosomes divide, 

 the body of the nucleus which retains its dis- 

 tinctness from the cytoplasm begins to pinch 

 in at the middle, and soon the separation of 

 the two nuclei is complete. A cell wall sepa- 

 rates the new cells at once. 



The author also discusses the relationship of 

 the Cyanophycese to the bacteria, holding that 

 they are closely related and that the latter too 

 probably have a nucleus similar to that de- 

 scribed. 



The book is, unfortunately, marred by an 

 excessive number of typographical errors. 

 The ten plates illustrating the book are finely 

 executed and are very helpful to the under- 

 standing of the subject. 



Eenest a. Bessey. 



Geology of Economic Non-metallic Minerals. 



By Francis Miron, C. E.* 



This little volume is published as one part 

 of the ' Encyclopedic Scientifique des Aide- 

 Memoire,' issued under the direction of IVI. 

 Leante, member of the Institute of France. 

 It is the fourth by the same author, the pre- 

 ceding volumes having dealt respectively with : 

 (1) Mineral oils, (2) subterranean waters 

 and (3) metallic minerals and mining. The 

 general object is to fxirnish a series of brief 

 hand-books describing the geological distribu- 

 tion, manner of occurrence and methods of 

 procuring and utilizing of the substances 

 treated of in each of the volumes. The pres- 



* ' Gisements Mineraux ; Stvatigraplilc et Com- 

 position,' par Francois Miron, Paris, Masson et 

 Cie, pp. 157. (Part of ' Eneyclopedie Scientifique 

 des Aide-M6moire.' ) 



