A,,ni, ii5] CrrOLOUICAL STUDIES ON CHRYSANTHEMUM. 49 



Chr. Leucanthemutn has 18, Chr. morifolium has 27, Chrv. 

 Decaisneanum has 36 (?), while Chry. acticum has 45 chromo- 

 somes.^ It is a noteworthy fact, that the numbers 18, 27, 36, 

 45 are all the multiples of 9. Similar cases were found in 



Musa by Tischler and in Viola bj' Miyaji. 



The sizes of the chromosomes of these plants are also different. 

 Generally speaking, the size of the chromosomes is inversely 

 proportional to the number of the chromosomes. The sizes of 

 the chromosomes of different plants with the same number of 

 chromosomes, however, are not always the same ; for example, 

 the chromosomes of Chr. nipponicum, carinatum, and coro- 

 narium are larger than those of Chr. japonicum, lavandulae- 

 folium, and Marschallii. 



II. Maiotic Prophase. 



The maiotic nuclear division was studied in the pollen 

 mother-cells of Chr. coronarium. The twelve figures in PI. II 2) 

 are concerned with the maiotic prophase of this plant. 



In the earliest stage, the parallel arrangement of the nuclear 

 thread is clearly visible, but this becomes obscure gradually in 

 the subsequent stages. The longitudinal splitting of the nuclear 

 thread occurs in the later synapsis. So in this stage, the para- 

 llel arrangement and the splitting are both visible (Fig. 6. PI. II.). 

 In the second contraction stage, the continuous single spirem 

 thread segments into 9 looped or ring-shaped portions ; thus 

 in the spirem stage the chromosomes are arranged end to end, 

 not side by side. 



According to the different authors, the explanations of the 

 parallel threads in the maiotic prophase are different. Some 

 authors regard them as the parallel arrangement of the whole 

 chromosomes, while others take them for the longitudinal split- 

 tings of the chromosomes themselves. 



1) The chromosome numbers were determined at the maiotic divisions of the 

 pollen mother-cells, thus the numbers above mentioned being those in the haploid 

 generation. 



2) Bot. Mag. Tokyo. Vol. XXIV, 1915, No. 338. 



