ISSN:
1432-0886
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary 1. All unbalanced samples of pollen from polyploid species ofTulipa, Fritillaria, Hyacinthus, andTradescantia have variable spiralisation at metaphase of their first mitosis, owing to the direct action of the individual genotype. 2. This variation reaches an extreme in two tetraploid species ofTulipa where the chromosomes are excessively contracted in certain pollen-grains. Correlated with the over-contraction we find (i) premature lapse of attraction between the chromatids, (ii) failure of synchronisation of the dividing centromeres which may be regular or irregular in effect, and (iii) formation of a hollow spindle. 3. Two forms of asymmetry occur in the anaphase spindle of the pollen-grain: (i) the one-sided arrest of movement and (ii) the bending of a long spindle. They are probably both due to the metaphase plate forming near the pollen-grain wall. 4. Exceptionally inTulipa the generative nucleus may divide in the pollen-grain instead of in the pollen-tube. InAmaryllis, the vegetative nucleus may divide a second time. This behaviour is a step away from the Angiosperm type and in the direction of the Gymnosperm type.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01271629
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