Zytologische Studien in der Gattung Populus L.

Dordrecht

1940

S. 131-182

94 Abb., zahlr. Lit. Ang.

Bandaufführung

141383

The male inflorescences of several species and natural hybrids of the genus Populus were fixed according to the method given in the table on p. 132, out with the microtome and the sections stained with haematoxylin according to Heidenhain. P. nigra L. showed the smallest number of divergences from the normal course of meiosis. During the prophase the nucleolus shows one or more buds (Fig. 1 and 2); in some cases one of them may attain the same size as the nucleolus itself (Fig. 3); at the junction of the two a pair of chromosomes is to be found. During the diakinesis 19 bivalents are usually observed; sometimes univalents are noticed (Fig. 5, 6, 7). One of the bivalents is usually situated upon the nucleolus, whilst another is conspicuous on account of its great size. In the metaphase-I 19 bivalents are found, which show a more or less distinct s'econdary association (Fig. 8, 9, 10). When secondary association reaches its maximum, the same grouping is always found, namely that according to the formula: A"A - BBB - CCC - DDD - EE - FF - GG - HH wherein the giant bivalent is represented by A"; to judge from its form and size, this A"-bivalent is probably formed by a fusion of 2 A-bivalents. According to this presumption the number of chromosomes would be 20 and during the metapase-I they are associated in 4 groups of two and four groups of three. If this secondary association, as in so many other plants, is to be regarded as an indication of secondary polyploidy, then the original basic-number would be 8 of which 4 chromosomes are duplicated and 4 are triplicated. According to this view, P. nigra would be a secondary polyploid, being partly tetraploid and partly hexaploid. The first and second divisions usually proceed normally. The formation of a restitution nucleus during the first division was observed once, as also the fusion of the two metaphase-II plates (Fig. 12). Curved cells are sometimes observed (Fig. 13). By far the majority of the tetrads are normal in shape (Fig. 14). P. nigra L. var. italica Du Roi shows approximately the same characteristics as P. nigra. The secondary association during the metaphase-I occurs more frequently and more distinctly (Fig. 17, 18, 19). Besides the tetrads some dyads and monads were noticed (Fig. 23, 24). P. brabantica HOUTZ. — a natural hybrid occuring in the Netherlands; probably a cross between P. marilandica Bosc. and P. serotina Hartig — shows many irregularities. During the prophase the nucleolus shows two small buds, one of which sometimes attains the size of the original nucleolus. In the diakinesis some of the chromosomes (the number differs in the different nuclei) are not paired (Fig. 25, 26). During diakinesis and the following stages the cytoplasm immediately surrounding the nucleus is usually more intensively coloured than the periferal cytoplasm (indicated in only a few of the drawings by dotted areas). After diakinesis either a normal metaphase plate is formed or the chromosomes are scattered through the spindle (Fig. 27, 28, 29, resp. Fig. 30,31).