1) Various karyotypes of two species belonging to
Brachycyrtis and seven species, six varieties and three races belonging to
Tricyrtis have been analysed from the view point of karyotype alteration. These plants all have 26 somatic chromosomes (2n=26=4L+22S) except
T. formosana var.
stolonifera (2n=25) and two hybrids between
T. hirta×
T. formosana and
T. hirta×
T. formosana var.
stolonifera (cf. Tab. 1, 2). The chromosome size in
Tricyrtis varies between the different species as regards both length and breadth and it is an interesting fact that as the chromosomes in a complement become shorter the satellites become smaller and disappear (cf. fig. 34).
2) Various combinations of the nucleolar chromosomes (including the SAT-chromosomes) are found in these species and their hybrids. Homozygous and heterozygous types of SAT-chromosomes in
Tricyrtis show the validity of Heitz's theory which assumes a correspondence between SAT-chromosomes and nucleoli at the telophase, while some plants of
T. formosana var.
stolonifera (2n=26=2L
n1+2L
n2+2S
t+20S) have only two short SAT-chromosomes and four nucleoli in the telophase and
T. formosana (2n=26=2L
n1+2L
n2+S
t+3S
n+18S) has only one short SAT-chromosome and one large and three small nucleoli in the telophase while
T perfoliata (2n=26=4L+4S
n+18S) has no SAT-chromosomes and four nucleoli in the telophase. In these cases many nucleolar chromosomes, besides the SAT-chromosomes, become attached to the nucleoli and this phenomenon namely mobilization of the nucleolar chromosomes may be explained on the basis of Matsuura's principle concerning the nucleolar chromosomes which assumes that first, every chromosome can be referred to as a “nucleolar chromosome” in the sense that it can produce nucleolus under certain specified conditions, and secondly, there is usually a differential rate in the capacity for nucleolusorganizing activity of the chromosomes within a complement.
3) Many hybrids between these plants the SAT-chromosomes and the nucleoli correspond in number, but the satellites of long chromosomes with small satellites from
T. hirta have disappeared in these hybrid in most cases. Such disappearance of the satellite or differential amphiplasty is clearly observed in
Tricyrtis hybrids as in
Crepis (cf. Navashin 1934).
4) The pollen grain mitosis in
T. formosana,
T. formosana var.
lasiocarpa and in hybrids between
T. hirta and
T. formosana (2n=26) was observed and, in addition to SAT-chromosomes, nucleolar chromosomes were found in the case of the hybrid i.e., long chromosomes as well as short SAT-chromosomes became attached to the nucleoli (cf. Tab. 7).
The disappearance of the satellite in hybrids, and mobilization of the nucleolar chromosomes in the root-tips and pollen grains are explained on the basis of the conception of “nucleolar chromosomes”.
In conclusion the writer wishes to express his sincere thanks to Professor Sinotô for his kind advice and valuable criticism throughout the course of his work.
A part of the expense of this work was defrayed out of a grant from the Japan Society for the Promotion of Scientific Research.
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