Chromosome behaviour in male and female individuals ofVallisneria spiralis andNajas marina

Abstract

The fact thatVallisneria spiralis pollen, as I have previously pointed out (l.c.) contains sometimes 8, sometimes 10 chromosomes (i.e. 8+1 double) is not, as I had supposed, a feature connected with the sex determination; both Jorgensen (l.c.) and I have found the same chromosome equipment (20 chromosomes) in the somatic nuclear plates of male and female plants. The appearance of 8 or 10 chromosomes is due to the fact that the double chromosome, at any rate in my material, is lagging behind the others at the reduction division and may quite frequently altogether fail to enter into the cell nuclei of the pollen, which will then have but 8 chromosomes. Such pollen must be regarded as incapable of functioning at all. The double chromosome in question appears on reduction division in pollen mother cells sometimes as a single element, sometimes as two separate ones, so that sometimes 9, sometimes 10 gemini can be observed. InNajas marina we similarly find, in somatic cells, sometimes 12, sometimes 14 chromosomes, as here also one pair of chromosomes may occasionally be united with another, thus reducing the number to 12. On reduction division, we find here as a rule only 6 gemini; Guignard, however (l.c.), has occasionally found 7. No difference in chromosome equipment of male and female plants could be found. TheNajas marina type investigated by me differs in regard to individual shape and size of the chromosomes from those previously investigated, and this to a conspicuous degree.