Marquette, JVIanifestations of polarity in plant cells wliicli usw. 301 
this, is the only attractive force which can be conceived as 
producing such figures as the dividing cell presents. So far little 
headway has beeil made toward a theory of cell-mechanics by the 
application of our knowledge of magnetic forces. It is a common 
weakness of the works of Ziegler, 1 ) Gallardo, 2 ) and Hartog 3 ) 
that they concern themselves almost solely witli a single stage of 
karyokinetic activity i. e. with the completed amphiaster. Success 
in producing by means of experimental arrangements a model in 
ironfilings of the same configuration as that sliown in some cases 
by the completed spindle would help little toward an understanding 
of the formation of such a spindle. 
Xeither the kinoplasmic nor the dynamic theory is in my 
opinion adequate to account for the behavior of the polar structures 
of Isoetes. They give no 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 luggest the central body as 
it is known for animals and lower plants. There is of course 
much difference of opinion regarding the natiire of the centrosome. 
its very existence as a structure of morphological or physiological 
value is still denied by some. 4 ) There is. liowever, 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 front one cell generation to anotheiy 
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; 
q Ziegler: Untersuchungen über die Zellteilung. (Verh. d. Deutsch. 
Zool. Ges. 1895. p. 62.) 
2 ) Gallardo, A.: Essai d’int^rpretation des figures karyokinetiques. (An. 
Mus. de Buenos Aires T. V. 1896. p. 10.) A propos. des figures karyokinetiques. 
(Compt. Bend, de Soc. Biol. T. LII. 1900. p. 732.) Les croisements des radiations 
polaires et linterpretation dvnamique des figures de karyokinese. (Ibid. T. LIII. 
1901. p. 454.) 
3 ) Hartog, 31.: The dual force of the dividing cell. (Proc. Boval Soc. 
B. Vol. 76. 1905. p. 549.) 
4 ) For evidence against the hvpothesis that the centrosomes are permanent 
cell Organs see 31 organ, T. H. The production of artificial astrosphaeres. 
(Arch. f. Entw.-3Iech. Bd. III 1896. p. 339.) The action of salt-solutions on the 
unfertilized and fertilized eggs of Arbacia and*of other animals. (Ibid. Bd. 3"III. 
1899. p. 448.) Wilson, E. B.: Experimental studies on cytology I. A 
cytological study of artificial parthenogenesis in sea-urchin eggs. (Arch. f. 
Entw.-3Iech. Bd. XH. 1901. p. 529.) 
5 ) See for example Boveri, Th. Zellenstudien. Heft 4. Über die Xatur 
der Centrosomen. 1901. 
