112 
PACIFIC SCIENCE, Vol. XVIII, January 1964 
TABLE 7 
Chromosome Configurations at Metaphase I of Meiosis in PMCs of 
a Within-Section Hybrid of Latourea, 2n = 37 
HYBRID 
D. atroviolaceum x D. macrophyllum 
CHROMOSOME CONFIGURATIONS 
1 7 2 — f~ 1 3 21 -J-I 62 -EI 3 ll-j-18 
22 2 r 
2 
of bivalents ranged from 7-0 with a mean of 
1.8, and that of univalents from 23-38 (Table 
8) . PMCs with no bivalents and 38 univalents 
were common. No definite metaphase plates 
were formed at metaphase I (Fig. 34). The 
movement of chromosomes to either pole at 
anaphase I was not orderly enough to produce 
the usual daughter nuclei, and consequently 
restitution was common for the majority of 
PMCs. The products of meiosis were mostly 
dyads with or without microcytes, but tetrads, 
monads, and triads were also observed (Table 
9) . 
DISCUSSION 
Meiosis in 11 species investigated was, as 
one might expect, regular. Also the within- 
section hybrids of Ceratobium exhibited 19 
bivalents regularly indicating a strong homology 
of species genomes within this section (Fig. 33). 
However, some morphological variation of 
chromosomes was evidenced through the forma- 
tion of heteromorphic bivalents in the species 
hybrids. The relatively high fertility that breed- 
ers encounter in these within-section hybrids 
reflects the strong homology of the parental 
genomes. 
The between-section diploid hybrids involv- 
ing the Ceratobium and Phalaenanthe sections 
indicated a greater divergence of parental gen- 
omes, for bivalents per PMC averaged from 
18.9 to 15.8. The fertility of these hybrids is 
generally impaired by the irregularity in meta- 
phase pairing. 
Meiosis in intra- and intersectional tetraploid 
hybrids throw additional light on the genome 
homology in Ceratobium and Phalaenanthe. The 
within-section tetraploid hybrid of Ceratobium, 
D. stratiotes x D. undulatum formed quadri- 
valents, bivalents, and univalents which is a 
characteristic chromosomal behavior of auto- 
tetraploids, while the between-section tetra- 
ploid hybrid of Ceratobium and Phalaenanthe, 
D. phalaenopsis x D. gouldii, behaved as a 
typical amphidiploid with the exclusive forma- 
tion of bivalents. It might be noted that the 
diploid counterpart of the within-section tetra- 
ploid showed good pairing at meiosis, while 
the diploid counterpart of the between-section 
tetraploid was irregular in meiosis. The inter- 
sectional diploid hybrids are generally low in 
fertility due to the poor chromosome pairing at 
metaphase, but doubling results in regularity 
in meiosis and the consequent restoration of 
TABLE 8 
Mean Chromosome Configurations at Metaphase I of Meiosis in PMCs of 
Between-Section Hybrids of Latourea, 2n r= 38 
MEAN 
NUMBER OF PMCS 
OBSERVED 
SECTION 
SPECIES CROSSED 
CONFIGURATION 
PER PMC 
Ceratobium x Latourea 
D. lasianthera x D. macrophyllum 
I6.31i-fl0.832 
30 
Phalaenanthe x Latourea 
D. phalaenopsis x D. New Guinea* 
34.28i+1.81 2 +0.32 3 
31 
* D. New Guinea is D. atroviolaceum x D. macrophyllum. 
