Place-constants for Aster prenanthoides

Shull, George Harrison (November 1904) Place-constants for Aster prenanthoides. Botanical Gazette, 38 (5). pp. 333-374.

DOI: 10.1086/328559


A second collection of heads of Aster prenanthoides Muhl. was made in 1903 from the same area at Clifton, Ohio, that supplied material for a quantitative study in 1900. The bracts, rays, and disk-florets were studied quantitatively, and the results compared with those of the earlier study. Twelve successive collections were made from the same plot, and it was found that the earliest collection had low mean numbers, that the mean values then leaped quickly to a maximum, falling gradually to near the end of the season, and that the last collection exhibited a rise, the rise in mean values at the beginning and at the end of the season being in disagreement with the conclusion reached in my earlier study. In general, the first head to bloom on any stem has the highest number of parts possessed by any head produced by that stem, and the last to bloom has the lowest number. The low mean numbers at the beginning of the season are due to the precocious flowering of the weakest individuals, and similarly the rise at the end of the season is due to the belated flowering of a few very vigorous individuals. Comparison of the results with those of 1900 show that the mean values in 1903 were 10-12 per cent. lower than in 1900, and that accompanying these low mean values there are a strong positive skewing of the curves, a remarkable rise in the coefficient of variability, and a considerable increase in the coefficient of correlation. The difference in the mean values for the two years is attributed to less favorable climatic conditions in 1903, chiefly to low temperature and low light-intensity in the month of June. The skewness is due to the unequal sensitiveness of individuals to changes of environment. It is positive because the proportion of conservative individuals is small In direct or physiological variation, "historic" skewness indicates great sensitiveness and "prophetic" skewness indicates slight sensitiveness to the changes of environment. The great increase in the coefficient of variability is due to an increase in the standard deviation and a decrease of the mean. The present coefficient of variability is not satisfactory in cases of skew variation, and the value of σ alone should be used as the measure of changes of variability in one and the same population. Changes in the coefficient of correlation may be due either to an actual change of correlation or to the introduction of a greater or less degree of heterogeneity. The latter is probably responsible for the changes noted in this species.

Item Type: Paper
Subjects: evolution
CSHL Authors:
Communities: Station for Experimental Evolution at Cold Spring Harbor
Depositing User: Matt Covey
Date: November 1904
Date Deposited: 17 Jan 2013 15:03
Last Modified: 01 Nov 2017 16:20

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