88 



Mr. K. P. Gregory. 



[Jan. 5, 



As the chromosomes move toward the equatorial plate the 

 longitudinal fission of each limb once more becomes clearly apparent, 

 so that, seen in face, the diverging daughter-chromosomes form a 



^-shaped body. A splaying of the ends of the rods at this or 



a slightly earlier stage often gives rise to those figures, not unlike 

 tetrads, which were assumed by Calkins'* to have an origin similar to 

 that of the tetrads characteristic of the heterotype division of, for 

 instance, Gryllotalpa, as described by Vom Eath. 



In the small chromosomes of the Ferns it is impossible, in the 

 majority of cases, to trace the presence of the original longitudinal 

 fission through the late prophase condition up to the beginning of 

 metaphase. Nevertheless, a study of the successive forms assumed by 

 the chromosomes indicates that the gradual obliteration is apparent 

 rather than real ; for it can still be recognised by means of the slightly 

 bifid ends of the limbs of the chromosomes. These appearances are 

 sufficiently convincing as to the correctness of the interpretation of 

 the so-called second longitudinal fission, as nothing more than a 

 reappearance of the original fission undergone by the spireme m the 

 early stages of prophase. 



The second (homotype) division follows very rapidly upon the com- 

 pletion of the heterotype division, and is provided for by the longi- 

 tudinal fission already noticed in the diverging chromosomes of the 

 heterotype division. 



The result is, therefore, a transverse true reduction division of the 

 bivalent chromosomes which characterise the heterotype division. 

 This work, therefore, provides an extension to another group of plants 

 of the results obtained by Farmer and Moore f in certain plants and 

 animals. 



It is not within the scope of the present paper to discuss the con- 

 siderations tending to support the belief in the universal occurrence 

 of a reduction division leading to the formation of the gametes. I 

 shall confine myself to a consideration of the significance of the 

 reduction division in connection with Mendelian segregation. 



Viewed from this standpoint the occurrence of a qualitative 

 reduction in plants as well as in animals is extremely important as 

 affording a possible provision for that purity of the gametes, in respect 

 of allelomorphic characters, which is demanded by Mendel's hypo- 

 thesis. 



The work of BoveriJ upon the qualitative differentiation of chromo- 



* " Chromatin Reduction and Tetrad-formation in Pteridophytes," ' Bull. Torrey 

 Bot. Club,' vol. xxiv, 1897, p. 101. 

 t Farmer and Moore, loc. ext. 



% " Mehrpolige Mitose als Mittel zur Analyse des Zellkerns," 'Verb., d. Phys. 

 Med. G-es. Wiirzburg,' 1902, vol. 35. 



