370 BULLETIN OF THE 



This differs in several particulars from the more recent account given 

 by Strasburger. 



In pollen mother-cells of Magnolia and Conifera a nuclear spindle has 

 also been seen by Tschistiakoff ; but the description is so confusud 

 through the introduction of imaginary " pronuclei " and " pronucleoli " 

 as not to be easily understood. In Magnolia, the equator and the poles 

 of the " pronucleus " become more compact. The equatorial lamella be- 

 comes broader, and exhibits a meridional striation. The substance of 

 the two poles represents the two prospective " pronuclei," during the 

 enlargement ctf which the striation becomes indistinct. Each of the two 

 resulting secondary " pronuclei " possesses two nucleoli. Each of the 

 " pronuclei " now divides, and so quickly that the act is almost simulta- 

 neous with the first cell division. 



In conifers after the nucleus has again assumed the condition of a 

 " pronucleus " there appear either one or six very fine protoplasmic 

 division-lamellae. This is an indication of the division of the " pronu- 

 cleus " either into two parts, or at once into four, which then have the 

 tetrahedral arrangement. Furthermore, both " pronucleus " and " pro- 

 nucleolus " are very peculiarly streaked upon the surface by a multitude 

 of serpentine lines consisting of more compact and lustrous portions of 

 the pronuclear substance.^ These lines become changed into broad, 

 compact, brilliant bands in the form of projecting meridians. The equa- 

 torial division-plate of lustrous protoplasmic corpuscles becomes broader. 

 Two protoplasmic regions, representing the prospective secondary nuclei, 

 now make their appearance at the poles. The streaked equatorial zone 

 persists for some time, but finally the streaks disappear, and the two 

 new pronuclei are separated by a wide zone of protoplasm. The "pro- 

 nuclei " are soon converted into nuclei. 



It will be seen that Tschistiakoff has not made a sharp distinction in 

 his description between cell plate and nuclear plate, and that the broad- 

 ening of the equatorial zone is the only thing that even hints at a mi- 

 gration of the halves of the nuclear plate. 



The criticisms of Auerbach (76") are directed toward the views ex- 

 pressed by Strasburger in the first edition of his celebrated work, " Ueber 

 Zellbildung und Zelltheilung." As that edition has not been formally 

 considered in the present paper, the reader is referred to the review of 

 the second edition, to be found at pp. 372 et seq. Auerbach has now 

 observed that the middle piece of his karyolytic figure is more spindle- 

 shaped than previously (1874) represented by him, and that it has a 



* Compare Flemming's ('78) descriptions of the nuclei of animal tissue-cells. 



