196 THE POPULAR SCIENCE MONTHLY. 



regular shrub, with many branches, terminated by large trusses of 

 bright-yellow llowers. Asa Gray says this plant is " common north- 

 ward " in wet ground, but I was not lucky enough to hit upon it dur- 

 ing my visit to America. However, I have seen living specimens from 

 Teesdale in England, and from them I perceive that, in general habit, 

 the plant greatly approaches the rock-roses {Ilclianthemum), which 

 grow in very similar situations. The leaflets of the shrubby poten- 

 tilla, long, narrow, and silky beneath, resemble, at first glance, the 

 leaves of the rock-roses, thus showing how similar conditions tend 

 everywhere to produce similar results, even when starting from the 

 most unlike organic forms to begin with. 



One other potentilla, the goose-weed or silver-weed {P. anserina), I 

 must needs mcution for form's sake, though I have nothing special to 

 say about it. It is a creeping species, growing close to the ground, 

 with long pinnate and prostrate leaves, silvery white below, with silky 

 down. Both in Europe and America it is very common as a road-side 

 weed, and in moist ditches ; but with us it is a weedier and scurvier 

 plant than with you — evidently a sufferer from our long civilization. 

 In America it grows mostly by river-banks and in brackish marshes ; 

 in Europe, it belongs rather to waste places and stony pastures than 

 to streams or mud-banks. Few temperate plants, however, have a 

 wider distribution. It is a circumpolar weed in both great continents, 

 extending through Russia and Siberia to Alaska and British America, 

 and it reappears once more, under like conditions, in the southern 

 hemisphere. Nothing kills it out, and it will bear both inundation 

 and trampling under foot to a greater degree than any other plant of 

 equal importance. 



The handsomest of your American potentillas, however, is the marsh 

 five-finger [P. comariim or palustris), a very bold and elegant water- 

 side plant, bluish-green in stem and leaves, and with loose corymbs of ex- 

 ceedingly pretty though dingy flowers. The calyx, inside, is lurid-red, 

 and the large petals are tinged with a gloomy and peculiar purple. 

 This fine ornamental plant loves cool northern bogs and marshes, being 

 common in Canada and in the Scotch Ilighlands. But what gives it 

 to me the deepest interest is its exact resemblance in hue and general 

 aspect to a purple avens ( Geum rivale), also common to either hemi- 

 sphere. Both are plants of the cold swamps and peaty places ; both 

 depend for fertilization upon water-side insects ; both have lurid-red- 

 dish calyxes, and both have large and dingy purplish petals. The 

 inference seems to me irresistible that the color has been evolved in 

 both cases by the special tastes of the upland water-creatures to whose 

 aid both owe the impregnation of their ovules. Indeed, it is often easy 

 thus to classify flowers functionally by their color and the tastes of 

 the particular insects that habitually visit them. In Europe, at least, 

 I believe the particular insect in this case to be Bhingia rostrata, 

 which I have observed in great abundance upon both flowers. Amer- 



