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PACIFIC SCIENCE, Vol XVIII, January 1964 
(Fig. 29) which often separated precociously. 
The synaptic force of the heteromorphic biva- 
lents was weak as evidenced by the precocious 
separation and the frequent close proximity of 
large and small univalents in a metaphase figure. 
D. superbiens has been considered a natural 
hybrid between species of the sections Phalae- 
nanthe and Ceratobium (Holttum, 1957). Its 
hybrid nature can be confirmed through the 
meiotic irregularity which is comparable to that 
of other intersectional hybrids. 
The products of meiosis were predominately 
tetrads (Table 9). These reflect the relatively 
high degree of chromosome pairing at meiosis. 
The percentage of spore tetrads was 90 or higher 
for all hybrids except D. phalaenopsis x D. 
gouldii (#2), which produced about 30% 
dyads and dyads with microcytes. 
Meiosis in Tetraploid Hybrids 
A within-section tetraploid, D. stratiotes x D . 
undulatum and a between-section tetraploid, 
D. phalaenopsis x D. gouldii, exhibited con- 
siderable difference in meiotic behavior (Table 
6, Figs. 30, 31). Metaphase I configurations of 
the within-section tetraploid were various com- 
binations of univalents, bivalents, and quadri- 
valents. The bivalents varied in number from 
38 to 32, and the quadrivalents and univalents 
from 2 to 0. Common configurations were 1 
IV + 36 II and 38 II. Quadrivalents involved 
the chromosomes of medium size. The two 
largest chromosomes which were presumed to 
be of D. undulatum origin exhibited a rather 
unusual behavior. They either paired with each 
other or, as can be seen in Figure 30, paired 
with small chromosomes to form the two ex- 
tremely heteromorphic bivalents. The two types 
of pairing occurred at about equal frequencies. 
The second largest pair of chromosomes pre- 
sumably contributed by D. stratiotes also be- 
haved in a similar fashion. The attenuation of 
the smaller chromosomes appeared to be a com- 
mon characteristic of these extremely hetero- 
morphic bivalents. Still other, though less con- 
spicuous, heteromorphic bivalents varying in 
number from one PMC to another were also 
observed. These variations in pairing of chromo- 
somes strongly suggest that autosyndetic as well 
as allosyndetic pairing occurs in this tetraploid 
hybrid involving two relatively closely related 
species. 
The between-section tetraploid hybrid, D. 
phalaenopsis x D. gouldii, showed normal meio- 
sis with 38 bivalents, and normal tetrads of 
microspores. The diploid hybrid of the same 
cross formed 19-13 bivalent associations at 
meiosis, but doubling in chromosome number 
restored complete regularity in meiosis, thereby 
revealing the amphidiploid nature of the tetra- 
ploid hybrid. 
TABLE 4 
Mean Chromosome Configurations at Metaphase I of Meiosis in PMCs of 
Within-Section Hybrids of Ceratobium, 2n =38 
HYBRID 
MEAN CONFIGURATION 
PER PMC 
NUMBER OF PMCS 
OBSERVED 
D. veratrifolium x D. undulatum, #1 
19.0 II 
25 
D. veratrifolium x D. undulatum, #2 
19.0 II 
25 
D. veratrifolium x D. stratiotes 
19.0 II 
25 
D. veratrifolium x D. tokai 
19.0 II 
25 
D. veratrifolium x D. schulleri 
19.0 II 
25 
D. veratrifolium x D. Taurus* 
19.0 II 
25 
D. stratiotes x D. tokai 
19.0 II 
25 
D. undulatum x D. gouldii 
19.0 II 
25 
D. taurinum x D. gouldii 
19.0 II 
25 
D. mirbelianum x D. johannis 
19.0 II 
25 
* D. Taurus = D. taurinum x D. undulatum. 
