114 
PACIFIC SCIENCE, Voi XVIII, January 1964 
Botanists always consider flower-characters more im- 
portant than vegetative ones when deciding on the 
limits of genera, for which reason the Vanda tribe has 
many genera and the Dendrobium tribe few. But it is 
fairly clear that some sections of Dendrobium are no 
more nearly related than some genera of the Vanda 
tribe; species of one section will often not cross with 
species of another, though intergeneric crosses in the 
Vanda tribe are common. 
Cytological evidences support Holttum’s 
views (Tanaka and Kamemoto, I960, 1961; 
Kamemoto and Shindo, 1962; Shindo and Ka- 
memoto, in press ) . The divergence between sec- 
tions of Dendrobium as measured by the degree 
of chromosomal homology is often much greater 
than that between some genera of the Vanda 
alliance. For example, chromosome homology 
among strap-leaved Vanda , Neofnetia, and As- 
co centrum or between terete-leaved Vanda and 
Luisia is much stronger than that among some 
sections of the Dendrobium genus. From the 
cytological standpoint, the entire Dendrobium 
genus with its 30 or more sections is some- 
what comparable to the entire Vanda alliance 
comprising numerous genera and therefore, if 
taxonomy of these groups were to be based on 
chromosome homology, the merger of several 
genera in the Vanda alliance and the elevation 
of several sections of the Dendrobium genus i 
to generic rank are indicated. 
Dressier and Dodson (I960) have concluded 
that there are no infallible "key characters” ; 
universally applicable for orchid classification. 
Emphasis on a single or limited number of 
taxonomic characters will inevitably lead to 
over-splitting or over-lumping, since different 
groups of orchids may have different rates of 
divergence of certain characters. It appears that 
for both Dendrobium and Vanda alliances, major 
revisions in classification based on an intensive 
study of morphological characters coupled with 
the accumulated knowledge on crossability and 
chromosome homology is highly desirable. 
SUMMARY 
Meiotic chromosome behavior was observed 
for species and intra- and intersectional hybrids 
involving Ceratobium, Phalaenanthe, and La- 
tourea of the genus Dendrobium . Meiosls was 
regular in all species, showing 19 bivalents at 
metaphase I. The within-section diploid hybrids 
of Ceratobium formed 19 bivalents as in the 
TABLE 9 
Sporad Formation in Between-Section Hybrids 
SECTION 
HYBRID 
SPORAD 
TOTAL 
Tetrad 
Tetrad +ms* 
Triad 
Dyad 
Byad-fms* 
Monad 
Phalaenanthe 
D. phalaenopsis 
x Ceratobium 
x D. undulatum 
95 
1 
1 
3 
100 
D. phalaenopsis 
x D. gouldii, #2 
D. phalaenopsis 
64 
4 
30 
2 
100 
x D. tokai 
D. phalaenopsis 
94 
3 
3 
100 
x D. taminum 
D. phalaenopsis 
95 
4 
1 
100 
x D. Johannis 
92 
8 
100 
D, phalaenopsis 
x D. veratrifolium 
87 
6 
1 
6 
100 
Phalaenanthe 
D. phalaenopsis 
x Latourea 
x D. New Guinea 
17 
2 
6 
56 
9 
10 
100 
Ceratobium 
D. lasianthera 
x Latourea 
x D . macrophyllum 
6 
2 
10 
64 
18 
100 
ms microcytes. 
