June, 1909.] Reduction Division in Hyacinthus. 
54i 
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¬ 
viduality. 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 stud}’. 
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 essentially 
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 definitely 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. 
