Complete analyses of pollen-mother-cell nuclei at first metaphase, percentage good pollen, pollen diameter and pollen-size distribution were determired for the following poplar species and natural hybrids: Populus grandidentata Michx., P. tremuloides Michx., P. eugenei Simon Louis, P. alba L., P. canescens Sm., natural hybrids of P. alba × P. grandidentata and of P. alba × P. tremuloides.Both of the P. alba and two of the four P. canescens trees examined were triploids (2n = 57) while all other trees examined were diploids (2n = 38). Meiotic observations on the natural hybrids indicated a high degree of homology between the chromosomes of P. alba and the native aspens (P. grandidentata and P. tremuloides), since 17 to 19 bivalents were usually found at first metaphase. In collections from one triploid P. canescens and two diploid alba-grandidentata hybrid trees, failure of a high proportion of the chromosomes to pair was attributed to genetic factors limiting pairing, rather than to non-homology.Pollen characters such as percentage good pollen, pollen diameter, and pollen size distribution were, in most cases, not indicative of the chromosome number or pairing relations at first metaphase. Consequently, triploids could not be detected by pollen observations under the conditions of this experiment. In spite of the lack of correlation between first metaphase and pollen observations, abnormally large pollen grains were observed in collections from several of the trees, and these were considered to contain the diploid or unreduced chromosome complement. The tendency for the poplars to produce unreduced pollen grains probably accounts for the number of triploid trees discovered in Canada and Sweden.
Natural hybrids of Branchiostegus japonicus and B. auratus landed at Nagasaki and Oita fish market
