I90 THE POPULAR SCIENCE MONTHLY. 



weed, and licrbaceous annuals were doubtless the earliest form of all 

 vegetation all the world over. Once more, the leaves are divided into 

 three leaflets ; and this type I take from its frequent recurrence not 

 only among the potentillas themselves, but in the strawberries, the 

 lady's-manlle, the simpler brambles, and many other species as well, to 

 have been the original type of foliage for the entire rose family. Fi- 

 nally, certain minute technical characters in the stipules and the styles, 

 with which I need not trouble you at the present moment, lead to the 

 conviction that we have here to deal to some extent with a fair repre- 

 sentative of the old ancestral potentilla form. 



The Norway potentilla, however, is distinctly weedy — that is to 

 say, it is one of those unpleasant, dusty-looking plants which loiter 

 about on the precincts of the road-sides and in the waste purlieus of 

 human cultivation. It attests its weediness by its bristly hairs, in- 

 tended doubtless to repel insects and to make it unpalatable to cattle 

 and horses. As its name implies, it is an Old- World form as well as a 

 native-born American citizen ; it is, in fact, a member of that ancient 

 circumpolar pre-glacial flora which was driven down from the once mild 

 and genial Arctic regions by the vast ice-sheet of the Glacial epoch to 

 occupy the plain-lands of either hemisphere in these our chilly and de- 

 generate modern summers. In Europe, however, it remains distinctly 

 a more northern type than with you in America, where it spreads as far 

 south as the Virginia hills. 



On the Alpine tops of the White Mountains I was lucky enough to 

 light upon another member of the potentilla group, not far removed in 

 essentials from the Norwegian weed, but infinitely prettier, more deli- 

 cate, and in a word less weedy all round. This is the plant which 

 Asa Gray identifies with our European Potentilla frigida of the Swiss 

 Alps ; and I, who have a pious horror of unnecessary splitting and re- 

 naming and tinkering, have not the slightest objection to the identifi- 

 cation in any way. But it is worth while to notice, what I often ob- 

 served of almost every American species said to be identical with those 

 of Europe, that the two plants are not absolutely the same : the time 

 that has elapsed since the Great Ice age effectually severed the two 

 continents has sufficed to produce distinct differences in nearly every 

 kind of plant or animal. The flowers in the American specimens are 

 smaller than in the Swiss, and the stems when full-grown are far less 

 hairy. 



Potentilla frigida exhibits all the common peculiarities of high 

 Alpine or Arctic plants. It is a dwarf form, not one fifth the size of 

 the Norway species ; it is tufted thickly on its low stems, and it has that 

 matted, close, creeping habit which I have already pointed out in this 

 " Monthly " as the distinctive feature of the glacial flora. It sticks still 

 to the three original leaflets, but its flowers, as is common in mountain 

 types, are far larger and handsomer than those of the wayside weed 

 with which we started our examination of the group. This Old-World 



