No. 463.] STUDfES ON PLANT CELL. VI. 



of the chromosomes in the mitoses of sporogenesis were longi- 

 tudinal with somewhat varying views, however, as to the exact 

 time when the two divisions take place. On the other hand 

 Ishikawa ('97), Calkins ('97), Belajeff ('98), and Atkinson ('99, 

 for Trillium) have claimed that the second mitosis presented a 

 transverse division. Dixon ('95, '96, : oo) and Schaffner ('97) 

 held a position apart from all these investigators, believing, that 

 the chromosomes of the first mitosis of Lilium resulted from 

 loops whose free ends became appressed or twisted together 

 finally separating at the angle of the loop and thus constituting 

 a transverse division in this first mitosis. These latter observa- 

 tions accord with the latest conclusions of Farmer and Moore 

 (: 03) and Strasburger (: O4b). Most of this literature is reviewed 

 in detail in Strasburger's paper of igooa. We shall omit an 

 historical discussion of this early work for the entire subject is 

 approached from quite a different standpoint in the series of 

 papers which have appeared in the past three years (1903-05) 

 and which give hope of much clearer information on the mitoses 

 of the spore mother-cell. 



The remainder of this treatment of " Reduction of the Chro- 

 mosomes " will take up the recent papers and try to show the 

 drift of the present investigations. These papers had not 

 appeared when the author described the behavior of chromo- 

 somes during mitosis in Section II (Amer. Nat., vol. 38, p. 445, 

 June, 1904) and presented the account of the spore mother-cell 

 in Section III (Amer. Nat., vol. 38, pp. 726, 740, Oct., 1904). 

 At that time it seemed probable that Strasburger's conclusions 

 of 1900 held true for all plants, namely, that the chromosomes 

 split longitudinally in both mitoses of sporogenesis as well as in 

 all other mitoses of the life history. Whejther these views may 

 have to be materially changed in the light of the most recent 

 work is now a matter of dispute. Yet the ground has shifted 

 so frequently in these perplexing problems that it is hard to feel 

 sanguine of final conclusions even in the hopeful situation of the 

 present. I shall take up the events of sporogenesis in order, 

 beginning with the growth period and synapsis and ending with 

 the two mitoses of the spore mother-cell. 



The growth period always extends over a considerable length 



