Cytology of conifers. II

Chromosome numbers inPodocarpus falcatus (2n = 24),P. gracilior (n = 12, 2n = 24),P. latifolia (n = 11, 2n = 22) and P. macrophyllus var.Maki (n = 19, 2n = 38) have been recorded. Nothing conclusive can be said as to whether the chromosome number has increased or decreased or both increased and decreased during the course of evolution of the genus

Biosystematics of the Sisymbrium irio Complex

S. irio Linn. is a polytypic winter annual which grows throughout the Panjab plains. It occurs in diploid, triploid, tetraploid, hexaploid and octoploid races. All these races get considerably modified in response to varying amounts of moisture and sunlight. The phenotypic plasticity has been studied experimentally using the conventional 'water-light' gardens

Basic chromosome numbers in Silene and Saponaria

During the course of a chromosome survey of the north-west Indian angiosperms, I have found two new basic numbers in the Caryophyllaceae of the Panjab Plains

Cytogenetics of tropical bulbous ornamentals VIII: Pollen grain mitosis in Zephyranthes puertoricensis

The immediate result of recombination during male meiosis within the complex interchange heterozygote polyploids in Zephyranthes could be assessed from the chromosomal constitution of pollen grains in one species with 2n=25. The numbers found in the pollen grains were n=1-16, 20 and 24. Considering n=12 (22.3%) as the haploid number, nearly 57.2% were subhaploid, out of which 19.6% had n=11. Occurrence of such a high proportion of subhaploid grains may be explained on the basis of the polyploid constitution (4x+1) of the species (x=6). In this sense, grains with a basic set of 6 chromosomes may be able to function. Therefore, in the real sense only grains with numbers less than 6 are submonoploid which constitute only 10.7%. In the subhaploid grains there was a preference for large and medium sized chromosomes, while in grains with higher numbers there was noted a tendency for smaller chromosomes to be represented more than once, indicating their non-disjunction during meiosis. Totally new types of nucleolar chromosomes emanating after recombination were also seen. This investigation has shown the extent of potential cytological polymorphism possible in heterozygotes like Zephyranthes puertoricensis. How much of this polymorphism is meaningful in creating the aneuploid pattern found in the genus, depends on the competitive advantage different numbers have during fertilisation vis-a-vis possibly similar polymorphism created during the female meiosis