106 COMPETITION AND CONSTANCY. 



the latter practically white. In nature, G. caespitosum is much more visited, 

 as it is a plant of open sunny slopes. Its flowers are larger and much more 

 conspicuous than those of Rubus strigosus, but are only about one-fourth 

 the size of the rose. They are also much smaller than the flowers of Aqui- 

 legia coerulea and the color somewhat less attractive, while the pollen is 

 much less abundant. Mertensia alpina possesses the advantage of blue 

 flowers, but the cluster is rather less conspicuous than a single geranium. 

 In the group of natural competitors, the heads of Aster bigelovi resemble 

 the flowers of geranium in size and color, but they yield more nectar and 

 pollen. Campanula rotundifolia, in spite of its deep blue color, produces 

 little pollen or nectar and moot pollinators ignore it. In both Allium 

 recurvatum and Heracleum lanatum, the smallness of the flowers is com- 

 pensated by their grouping in umbels, though even this is little effective 

 in Heracleum. The pink flowers of Allium produce an amount of nectar 

 and pollen that is out of proportion to their size. Of the competitors 

 with zygomorphic flowers, Pentstemon secundiflorus and P. barbatus have 

 larger and more brilliant flowers, and the cluster is larger and more vivid 

 in Castilleia miniata, while the chief asset of the small, dull flowers of 

 Scrophularia nodosa lies in the abundant nectar (plates, 3 7, 11, 12, 13, 

 and 14). 



Experiments. — Table 73 deals with the competition between the two 

 species of Geranium in various installations, table 74 with competition be- 

 tween Geranium and other genera, and tables 75, 76, and 77 with group 

 competition. 



Although Geranium caespitosum yielded 277 visitors to 155 for G. richard- 

 soni, in competition with each other, they are more nearly equal in attrac- 

 tiveness than this would indicate. This difference is more than accounted 

 for in the behavior of Prosopis, which preferred caespitosum in the ratio of 

 184:28, chiefly when this species was the standard. The two were practi- 

 cally equal when both were used in the form of bouquets, and they changed 

 rank in two successive periods in which they alternated as standards, the 

 respective ratios being 88:9 and 83:10. This equality is further indicated 

 by their behavior in competition with Rubus strigosus, though the conditions 

 were not precisely comparable in the different experiments. When plants 

 were compared, A pis was perfectly constant to the raspberry, but in all 

 other cases it exhibited a practically exclusive preference for the standard 

 plant, going to richardsoni, caespitosum, or strigosus as each took this role. 

 Between richardsoni and strigosus as plants, Prosopis gave a ratio of 42:1, 

 while between bouquets of G. caespitosum and Rosa the ratio was 28:0. 

 The honey-bee behaved similarly in the latter choice, while for Bombus the 

 preference was reversed, namely, 0:29, as it was likewise for Megachile 

 and Anthophora. However, Aquilegia in a mixed boquet was as attractive 

 as standard G. caespitosum, while the associated Mertensia alpina received 

 but one visit. It is interesting to note that Andrena crataegi was the only 

 visitor to both Geranium and Aquilegia in this experiment. 



The size of the flowers differs so much in this group that exact comparisons 

 are difficult. In spite of the size of the clusters, however, the pinkish or 

 white flowers of Allium and Heracleum were obviously at a disadvantage. 

 The flowers of Geranium and Campanula and the heads of Aster are somewhat 



