Marquette, Manifestations of polarity in plant cells whicfa usw. 30J 



this, is the only attractive force whicli can be conceived as 

 producing such figures as the dividing cell presents. So far little 

 headway has been made toward a theory of cell-inechanics by the 

 application of our knowledge of magnetic forces. It is a common 

 weakness of the works of Ziegler, 1 ) Gallardo, 2 ) and Eartog 8 ) 

 that they concern themselves almost solely with a Single stage of 

 karyokinetic activity i. e. with the completed amphiaster. Success 

 in producing by nieans of experimental arrangements a model in 

 ironfilings of the same configuration as that shown in some cases 

 by the completed spindle would help little toward an understanding 

 of the formation of such a spindle. 



Neither the kinoplasmic nor the dynamic theory is in my 

 opinion adequate to account for the behavior of the polar structures 

 of hoetes. They give 110 explanation of the perfectly regulär 

 division of these structures preparatory to cell division nor for 

 their unvarying position exactly at the poles of the spindles. The 

 facts which have been brought out as to the structure, position, 

 and behavior of these bodies all point to them as selfperpetuating 

 and perhaps permanent organs of the cell, organs which in their 

 behavior during cell division at once suggest the central body as 

 it is known for animals and lower plants. There is of course 

 much difference of opinion regarding the nature of the centrosome, 

 its very existence as a structure of morphological or physiological 

 value is still denied by some. 4 ) There is. however, a large amount 

 of apparently unquestionable evidence 5 ) which goes to show that 

 in some cases at least the centrosome is an organ of the cell 

 which passes continuously from one cell generation to another, 

 reproducing itself by division. Likewise there is a general consensus 

 of opinion that the centrosome is most intimately connected with 

 spindle formation and cell division. 



The polar structures of Isoetes are of sufficient size to be 

 readily distinguished at any period in the existence of the cell; 



a ) Ziegler: Untersuchungen über die Zellteilung. (Verh. d. Deutsch. 

 Zool. Ges. 1895. p. 62.) 



2 ) Gallardo, A.: Essai d'interpretation des figures karyokinetiques. (An. 

 Mus. de Buenos Aires T. V. 1896. p. 10.) A propos. des figures karyokinetiques. 

 (Compt. Rend. de Soc. JBiol. T. Lü. 1900. p. 732.) Les eroisements des radiations 

 polaires et Interpretation dvnamique des figures de karyokinese. (Ibid. T. LIII. 

 1901. p. 454.) 



3 ) Hartog, M. : The dual force of the dividing cell. (Proc. Boval Soc. 

 B. Vol. 76. 1905. p. 549.) 



4 ) For evidence against the hypothesis that the centrosomes are permanent 

 cell organs see Morgan, T. H. The productiou of artificial astrosphaeres. 

 (Arch. f. Entw.-Mech. Bd. III 1896. p. 339.) The action of salt-solutions on the 

 unfertilized and fertilized eggs of Arbacia and'of other animals. (Ibid. Bd. VIII. 

 1899. p. 448.) Wilson. E. B.: Experimental studies on cytology I. A 

 cytological study of artificial parthenogenesis in sea-nrchin eggs. (Arch. f. 

 Entw.-Mech. Bd. XII. 1901. p. 529.) 



6 ) See for example Boveri, Th. Zellenstudien. Heft 4. Über die Natur 

 der Centrosomen. 1901. 



