June, 1909.] Reduction Division in Hyacinthus. 541 



he finds the spirem varying in thickness in different parts, 

 exhibiting constrictions and dilations indicating more or less 

 clearly where segmentation into chromosomes will take place. 

 He says there is nothing to indicate that the successive chromo- 

 somes are members of a pair, but one chromosome frequently 

 swings around and pairs with its neighbor on the skein. He 

 concludes: "We do not really have, then, a transverse division 

 of chromosome bivalents, but a separation of whole (somatic) 

 chromosomes." 



One of the most interesting and prominent features in the 

 reduction karyokinesis of the hyacinth is the marked individual- 

 ity of the bivalent chromosomes. After the formation of the 

 loops, a transverse breaking of the continuous spirem takes place 

 by which they are separated (fig. 16.) The contracting loops 

 show a tendency toward definite size and shape and when the 

 chromosomes have their final form they show a striking indi- 

 vidualitv. There are two comparatively small chromosomes, 

 a third of medium size and another only a little larger, while the 

 remaining four are of giant proportions when compared with the 

 two smallest. Of the two medium sized chromosomes, one is 

 generally somewhat heart- or v- shaped, while the other is a 

 more or less irregular mass usually without two projecting limbs. 

 Of the four large ones, two in favorable sections, always show a 

 prominent twist while the other two show a more compact and 

 regular form. These shapes and sizes were noted in many differ- 

 ent nuclei (figs. 18-22). 



Fine threads were often present, extending from the loops 

 to the nuclear wall or connecting the loops themselves. These 

 threads were also present after the separation into chromosomes 

 (fig. 17). 



The formation of the spindle and the subsequent stages were 

 not included in the study. 



It will be evident from an examination of the figures, that 

 the pairing which takes places in the formation of the bivalent 

 or reduction chromosomes, is between univalents of essentiallv 

 the same shape, size and activity. There can be little doubt but 

 that these similar conjugating chromosomes represent a pair, 

 the one maternal and the other paternal. The equivalent 

 maternal and paternal chromosomes are, therefore, of essentially 

 corresponding shapes and sizes. To determine definitelv by 

 observation whether all the maternal or paternal chromosomes 

 go to a single pole, will require cases in which a difference in 

 character between the two can be determined. 



