dized and in those cases where complete incompatibility 
exist, such as Datura ceratocaula, hybrids have been ob- 
tained by embryo-dissection and culture (5, 18). Blakes- 
lee (4) has found that in all Datura hybrids the degree 
of fertility varies; however, all the chromosomes show a 
high degree of synapsis during meiosis resulting in the 
formation of varying numbers of closed bivalents or 
multivalent configurations and a complete absence of 
univalents. These findings led him to conclude that the 
differences in the genomes of the various species are due 
mainly to reciprocal exchanges of the ends of the chro- 
mosomes without affecting much of their structural 
similarity. 
Even with the use of the embryo culture technique, 
Brugmansia X Datura hybrids are extremely difficult 
to produce. Carson (8) in 1945 was able to make the 
hybrid Datura inowvia (female) X Brugmansia suaveo- 
lens, and Joshi (11) in 1949 the hybrid D. ¢nowia (female) 
x B. aurea (this was mistakenly identified by Joshi as 
B. Roset). In both cases, the hybrids were completely 
sterile. Joshi’s studies showed the presence of a large 
number of univalents and only a few bivalents during 
meiosis in these hybrids. He concluded that the ex- 
tremely poor synapsis in the hybrids is indicative of great 
structural differences in the two parental genomes. 
Conclusion 
The question of whether Brugmansia should be re- 
garded as a distinct genus or as a subgenus or section of 
Datura has long been a matter of debate among taxono- 
mists. Kvidence based on anatomical, morphological, 
ecological, and genetic considerations indicates that the 
two have evolved independently and no intermediate or 
ancestral forms are known to exist. The highly special- 
ized semi-aquatie species Datura ceratocaula cannot be 
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