88 THE BOTANICAL 31A0AZINE. [Voi. xxn. Ko. 256. 



in every year, and so the more vigorous is the plant. Indeed, 

 in spite of its single-headedness,'^ there was so remarkable a 

 difference in flowering season that we could see the yellow 

 heads for more than fourty days. 



In addition to this, there are still other factors to be noticed, 

 namely the fertility of soil and the general condition of vegeta- 

 tion. I have selected for the collection three places where the 

 plant predominantly grows, namely the western inner wall of 

 the crater, and the estern radial valley of the peak and its 

 northern slope, the former including the area of about 20 to 

 60 m., and the latter two, of about 100 to 250 m. below the 

 summit, I will call hereafter these three places, the crater, the 

 valley and the slope. In the crater and the valley there can be 

 found no perceptible difference of vegetation, but on the slope, 

 which is the northern border of the valley, (its southern border 

 is densely covered by bamboo-grasses) the vegetation is very 

 poor. Its upper part is occupied by a scanty growth of bam- 

 boo-bushes, and its lower part, on account of snow-slip, is 

 almost sterile, exposing the greater part of the naked volcanic 

 detritus, so that a glance on the plants growing there gives 

 clearly the impression of weaker growth. 



Arnica unalaschcensis is thus a very interesting object for 

 the study of variation, being indifferent to the seasonal and 

 corresponding meristic changes of rays on account of its single- 

 headedness, and its growing region being subjected to two con- 

 ditions, namely the regular progression of snow-thawing and 

 the fertility of soil, the former of which being the principal 

 condition for the change of flowering season. And it is more 

 likely to gain valuable results from the collection of material 

 under known conditions than from at-random collection, as 

 Shull already mentioned.^^ 



I visited these places for the collection four times within a 

 month. On my first visit on July 29, I found the plants in full 



1' Seven specimens were found with one or two lateral heads throughout my 

 collections. They were seen witli very small number ot" rays in their lateral heads, 

 and such stocks were rejected from tl:e material used. 



2) Shull, 1.c. p. 150. 



