1928] Wexelsen: Chromosome Numbers and Morphology in Trifolium 



361 



The species can be grouped as follows according to chromosome size, 

 the species in each group being arranged according to increasing size 

 of the chromosomes: 



SMALL 



1. T. variegatum 



2. T. repens var. sylvestre 



3. T. minus {^.) 



4. T. wormskjoldii 



These groups are not sharply set apart ; if all the chromosomes in all 

 the complexes are arranged according to size they will form a con- 

 tinuous series, but if one looks at the chromosome complexes as such, 

 the complexes in the small groups are distinctly smaller, and those 

 in the larger group larger, than the complexes in the medium group. 

 It is not contended that these groups have any phylogenetic signifi- 

 cance, but they may serve to give a picture of the situation. 



Bleier (1925) discusses the question of chromosome size in relation 

 to chromosome number, nuclear size, and plant size. His discussion 

 is based on the size of the bivalent chromosomes at the heterotypic 

 metaphase and on measurements of the nuclear diameter of the pollen 

 mother cells at the synaptic stage. As is pointed out by him there is 

 great variation in the size of the metaphase chromosomes within a 

 species. The same was found in T. alexandrinum in which a large 

 number of metaphase plates were studied. In the same way the 

 chromosomes at the somatic metaphase show some variation within the 

 species (see figs. 2a and 2h of T. pratense), but the variation is less 

 than in the pollen mother cells. Bleier makes the following statements 

 regarding chromosome size in Trifolmm: 



1. Species with the same number of chromosomes have chromosomes of different 

 size. 



2. The nuclear volume is not dependent upon the number of chromosomes, but 

 on the mass of chromatic substance. 



3. There is no correlation between chromosome number and plant size, but 

 species with a larger nuclear volume have larger growth than species with small 

 volumes. 



