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PACIFIC SCIENCE, VoL XVIII, January 1964 
TABLE 1 
Species Investigated or Involved as Parents of Hybrids 
SECTION 
SPECIES 
GEOGRAPHICAL DISTRIBUTION 
Ceratobium 
D. gouldii Rchb. f. 
D. grantii C. T. White 
D. Johannis Rchb. f.* 
D. lasianthera J. J. S.* 
D. mirbelianum Gaud.* 
D. schulleri J. J. S.* 
D. stratiotes Rchb. f. 
D. strebloceras Rchb. f. 
D. taurinum Lindl.* 
D. tokai Rchb. f. 
D. undulatum R. Br. 
D. veratrifolium Lindl. 
Thursday Island 
New Guinea 
Northern Queensland, Thursday Island 
New Guinea 
New Guinea 
New Guinea 
Celebes 
Sunda Islands 
Philippines 
Fiji 
Northern Queensland, New Guinea 
New Guinea 
Phalaenanthe 
D. bigibbum Lindl. 
D. phalaenopsis Fit2g. 
Cape York Peninsula, New Guinea 
Moluccas to northern Queensland 
Latourea 
D. atroviolaceum Rolfe* 
D. macrophyllum Lindl. 
New Guinea 
New Guinea to Java 
* Involved as a parent of hybrid investigated. 
might well serve as "markers” for the genome 
of D. undulatum . 
D. strebloceras possessed two pairs of chromo- 
somes which were larger in size than the rest 
of the complement and were strongly heteropyc- 
notic at prophase of meiosis. D. stratiotes showed 
similar characteristics, but with additional pairs 
of large bivalents. D. veratrifolium, D. phalae- 
nopsis ( Fig. 25) and others also possessed sev- 
eral large bivalents but of graded size and 
heteropycnosis. 
Meiosis in Within-Section Diploid Hybrids of 
Ceratobium 
The 10 intrasectional diploid hybrids of Cera- 
tobium (Figs. 13, 14) investigated showed 
regular pairing at meiosis ( Table 4 ) . However, 
some of the bivalents were conspicuously hetero- 
morphic. This might be expected on the basis of 
the morphological variations of chromosomes of 
the different genomes. 
The number and form of heteromorphic pairs 
varied from one hybrid to another depending 
on the parentage. The two hybrids of D. un- 
dulatum — D. veratrifolium x D. undulatum and 
D. undulatum x D. gouldii — showed a markedly 
heteromorphic bivalent involving the large 
"marker” chromosome of D. undulatum. Highly 
heteromorphic bivalents were also observed in 
D. stratiotes hybrids. Four such bivalents were 
observed for D. stratiotes x D. tokai, and four 
to five in D. veratrifolium x D. stratiotes (Fig. 
27). The smaller of the bivalent chromosomes 
often appeared as a chromatin thread pulled out 
from the darkly stained larger chromosome. 
These bivalents characteristically separated pre- 
cociously. 
Meiosis in Between-Section Diploid Hybrids of 
Phalaenanthe and Ceratobium 
In addition to the natural hybrid, D. super - 
biens (Figs. 17, 18), six diploid intersectional 
hybrids involving Phalaenanthe and Ceratobium 
(Figs. 15, 16) exhibited similarly irregular 
meiotic behavior (Tables 5, 9, Figs. 28, 29). 
Both bivalents and univalents were observed, 
and occasionally some trivalents probably re- i 
suiting from the chance association of sticky 
chromosomes were also seen. 
The bivalents in PMCs varied in number 
from 19 to 13 and the univalents from 2 to 12. 
Most of the PMCs formed 19-16 bivalents and 
0-6 univalents. As indicated in Table 5, the 
mean number of bivalents was highest (18.9) 
