194 ^^^ POPULAR SCIENCE MONTHLY. 



the Mediterranean to the shores of the Atlantic, and, crossing the ocean 

 with seed-corn and fodder crops, have clogged the steps of the intru- 

 sive white man through all his colonies and settlements elsewhere. 

 These cosmopolitan weeds succeeded in America to the soil once cov- 

 ered by forest-trees, whose indigenous undergrowth could not stand 

 the garish sunlight of the open clearings. But nowadays, the weed- 

 ier types of the Western prairie-belt are moving eastward, as farms 

 move west ; and being accustomed by nature to open plaius, they will 

 probably, in many cases, succeed in establishing themselves side by 

 side with the older plagues of the long-suffering farmer. Potentilla 

 paradoxa is one of the first crop of these weedy immigrants, and its 

 appearance already on the shores of Lake Ontario is the signal for its 

 future advance in a formed phalanx against the tilled fields of New 

 York and New England. 



This Western immigrant departs widely in one respect from the 

 type of all the potentillas we have yet considered, and that is in the 

 arrangement of its five, seven, or nine leaflets. In the true cinque- 

 foils, and all their like, the leaflets are arranged, as we say, palmately 

 — that is to say, all start together, like the lobes of a horse-chestnut 

 leaf, from one point. In the P. paradoxa they are arranged pinnately 

 — that is to say, they start in opposite pairs or singly, from a common 

 midrib, like the barbs of a feather or the leaflets of a locust-leaf. 

 The same arrangement, a more convenient one for long leaves, reap- 

 pears in P. Pennsylvanica, which (in spite of the name incorrectly be- 

 stowed upon it by Linnaeus) is a Northwestern species. But as I have 

 not seen this last-named plant in the living state, and as I do not like 

 to write about what I have only examined in a dried-up herbarium (a 

 bad habit of the old-fashioned, purely structural botanists), I will say 

 no more at present about it. 



On the rocky hills of the North and West there occurs in July a 

 rather pretty, half-shrub-like potentilla [P. arguta), Avhich presents 

 several other interesting peculiarities. This plant has brownish, hairy 

 stems, covered with a viscid, clammy exudation, something like that 

 which covers the young branches and buds of the clammy rose acacia 

 (Hobinia viscosa). As I observed that insects are often caught in this 

 clammy secretion, exactly as in the case of the common catcbflies 

 {Sllene noctiflora Virglnica, regia, etc.), I have not the least doubt that 

 the potentilla eats and digests the creatures it entraps, in order to 

 supply it with nitrogenous material for its own pollen, ovules, and 

 seeds. This is the more probable, as the clamminess increases near 

 the flower-buds and blossoms, and is scarcely at all noticeable near 

 the base of the stem, llow the potentilla digests its food I do not 

 know, but long observation has fully convinced me that whenever a 

 plant has viscid, glandular hairs or secretions upon its penduncles, 

 pedicels, calyx, and flower-buds, it is invariably an insect-catcher, 

 and an insect-eater too. The flowers are the part that require the 



