734 '^^^ AMERICAN NATURALIST. [Vol. XXXVIII. 



phytes developed without centrosomes, while illustrating a proc- 

 ess of spindle formation along somewhat different lines. Smith 

 distinguished a zone of kinoplasm around the nucleus previous 

 to spindle formation. This zone became granular, and then the 

 granules arranged themselves in rows to form fibrillas (Fig. 13 d), 

 which, however, did not extend into the cytoplasm radially, but 

 lay generally parallel to one another, so that the spindle appeared 

 bipolar from the beginning (Fig. 13 ^). One pole of the spindle 

 was generally formed considerably in advance of the other (Fig. 

 13/). The fibers did not meet at a common point but over a 

 broad area, and there were no centrosomes. There is, then, nor- 

 mally no multipolar stage in Osmunda, although tripolar spindles 

 (Fig. t3_g-)were occasionally found. During anaphase secondary 

 fibers were put forth from the vicinity of the daughter nuclei and 

 these met in the equatorial region of the cell. The spindle of 

 the second mitosis was formed exactly as in the first. After this 

 division the four granddaughter nuclei lay connected 'with one 

 another by six spindles (two primary and four secondary). Cell 

 plates were laid down in the equatorial regions of these spindles 

 so that the protoplasm became divided simultaneously and sym- 

 metrically into tetrahedral spores. 



The studies of Calkins ('97) and Stevens ('98(7) were chiefly 

 upon the division and distribution of the chromosomes in con- 

 nection with reduction phenomena. Calkins believed that the 

 processes of sporogenesis followed the same course as the matu- 

 ration of sexual cells in animals, with a transverse division to 

 give a qualitative reduction in Weismann's sense. Stevens dis- 

 agreed with Calkins in several particulars, holding that the 

 reduction was merely quantitative. . Reduction phenomena in 

 plants is now much better understood than at the time of these 

 papers which dealt with plants much more difficult to study than 

 some other forms {e. g., types of the Liliacese). We shall con- 

 sider the subject in Section V, but may state now that Calkins' 

 conclusions have not been sustained. 



Strasburger (:oo) gives considerable attention to spindle 

 formation in his well known review and critique of cytological 

 literature. He proposes the following classification of spindles 

 in higher plants which lack centrosomes. Those that pass 



