MAY 1908.1 KORIBA.— VARIATION IN THE BAY-FLOWERS. 87 



show the seasonal change without any disturbance of the 

 enviromental conditions, for the velocity of development of 

 heads and the corresponding meristic change of their rays depend 

 on their position in branches. This is perhaps due to the differ- 

 ence of distribution of nourishment, and so the earlier the head 

 blossoms, the larger is the number of parts, and vica versa.'^ 



But we should still consider the external influences, especially 

 that of the climatic change, which evidently must affect the 

 organs in its early stage of development.-^ And if a change has 

 thus occurred in one part of a plant by an external cause, this 

 again introduces the disturbance to all other parts of branches 

 where the organs are not yet formed, in such a way as it was 

 called the correlative mosaic work by Haacke.^^ 



Thus in the multicipital Compositae, the inner tendency' of 

 variation of rays is intricately affected by the fluctuation of ex- 

 ternal factors, so that, unless we treat only with the primary 

 heads, the influence of each factor on the variation is not easy 

 to determine. On the other hand in the single-headed Com- 

 positae, the head being reprCvSentative of that individual stock, 

 not only the variation of rays, but also the deviation of 

 flowering season must depend entirely on the external condi- 

 tions, so that, if we know the actual conditions, we can 

 compare the results hand in hand with them. 



In the case of Arnica unalaschcensis the difference of snow- 

 thawing by different parts of the mountain as was already 



mentioned in the peak of such a height it thaws from up 



to downward, from slope to valley is one of the great 



factors which determines not only the flowering season, but 

 also the vigorousness of plants. The earlier the snow thaws, 

 the earlier it blossoms and the longer is the duration of growth 



1) De Vries, Mutationstheorie. Ed. I, Leipzig, 1901. p. 544-5. Shull, A 

 quantitative Study of Variation in the Brae's, Rays, and Disc Florets of Aster Shortii 

 etc. Amer. Nat. Vol. 36, 1902, p. 150. 



2) De Vries, I.e. p. 99, 371. 



3) Haacke, Entwickelungs-mechanislie Untersuchuugen. I. tJber numerische 

 Variation typisclier Organe and korrelative Mosaikarbeit. Biol. Centralbl. Bd. 16, 

 1896, p. 496. 



