694 



GARDEPiERS' CHRONICLE 



Plant Immigrants 



WILLARD N. CLUTE 



IT is a fact well known to every rambler countryward, 

 that the flora of any region consists of two elements ; 

 a rather stationary native element and a more mobile, 

 aggressive, exotic one. The native element is stationary 

 because each member of it has found, after ages ot 

 struggle, the niche in the landscape which it can best fill 

 and has settled down to occupy it, secure against nearly 

 all comers. The exotic flora comes from the ends of the 

 earth and, like other immigrants, is ever seeking a place 

 in which to colonize. Its members diiYer from ordinary 

 plants in that they have a strong disposition to extend 

 their area of occupation coupled with the ability to do it. 

 All plants have a natural tendency to spread, but it is 

 only when they become aggresive enough to overcome 

 the' original tenants of the soil that they attract our atten- 

 tion. Then we call them weeds. 



Not all weeds are exotic, however. Such of our na- 

 tives as have the ability to conquer new territory may 

 become as pestiferous weeds as any. The evening prim- 

 rose, the cockle-bur, the bindweed and the smartweed arc 

 good examples. Nor must we overlook, in this connec- 

 tion, the career of the prickly pear in Australia or the 

 ditch moss (Elodea) in European waters. The latter is 

 a harmless and inconspicuous inhabitant of ponds and 

 slow-moving streams on this side of the world, but 

 abroad it fills up the water-courses and is so troublesome 

 that they call it American weed. 



TJie parts of our flora least atiected by weeds are the 

 woodlands. In all our history there appears never to 

 have been a tree immigrant able to crowd out our native 

 species. The Ailantliiis, or .Chinese tree-of-heaven, 

 shows a tendency to spring up in waste grounds, as do 

 various native species, for that matter, but it has not yet 

 attempted to invade the forests. 



Most of our invaders are herbs. They are most abun- 

 dant along roadsides, on railway embankments and in the 

 fields, partly because they have been recruited from such 

 places in other parts of the world and partly because 

 they move most rapidly along the regular routes of travel. 

 There have been, of course, invasions from various direc- 

 tions but the prevailing direction has been ever westward 

 as it has in the case of man. himself, who might possibly 

 be considered a weed by an impartial observer. 



The exotic plants are usually our worst weeds because 

 their fighting qualities have been developed by perennial 

 conflict with the cultivators of the soil. No plant could 

 sur\'ive the age-long contest unless it possessed a vigorous 

 constitution, to say the least. Among the qualities that 

 make for weediness are the capacity for rapid growth, 

 the ability to endure drouth and to grow in poor soil and 

 the power of producing vast numbers of seeds well fitted 

 for rapid distribution. We sometimes fail to realize how 

 rapidly some of these plants multiply. A single plant of 

 pigweed has been found to produce 85.000 seeds, the 

 crab-grass is reported to do even better and the yellow 

 foxtail tops the record with 113.000 seeds. In addition 

 to seeds, many species have vegetative means of reproduc- 

 tion. The Canada thistle and quack grass have deep root- 

 stocks from which new liranches are sent up when the 

 first are cut ofif. The purslane has no rootstock but it is 

 so fortified against adversity that if cut ofif after it is in 

 bloom it can go on fruiting independent of anv connection 

 with the soil. 



Some European weeds have been with us so long that 

 we have alnK)st forgotten their foreign origin and regard 

 them as nali\es. The thistle, mullein, dandelinn and liur- 



dock seem part of the original population. There are 

 others, however, whose arrival is still so recent that men 

 in middle life can remember their first appearance. The 

 tumbling mustard, now so widespread, is one of the most 

 recent. It is less than twenty-five years since the devil's 

 paint-brush began to redden the hills of New York and 

 Pennsylvania and the prickly lettuce did not become a 

 weed in many places before 1890. No doubt there will 

 be many more to follow. The ballast ground along our 

 coasts where ships are wont to discharge their surplus 

 material of this description has yielded specimens of prac- 

 tically every pernicious weed in the world. Many of 

 these only wait an opportunity. They often need some 

 special condition to get started but afterward make great 

 headway. 



The fact that a given species has spread over an ex- 

 tensive region, however, is no indication that it will con- 

 tinue to spread. Often what threatens to be a particularly 

 troublesome weed will after a time subside into com- 

 Ijarative harmlessness. Weeds have their predilections 

 like other plants and must often surrender to natural con- 

 ditions. The tumble weeds were once the terror of the 

 l>lains. Instances are on record of their stopping trains 

 1:)V sheer numbers. Railway cuts were often filled with 

 them. But when man began to fence the plains, their 

 triumphs were over. Their last stand is in the desert and 

 here sheep and goats make short work of them. Another 

 plant that has gone west to experience greater triumphs 

 is the caltrop. It thrives along sandy roadsides and is 

 ever on the increase, aided thereto by its sharp pointed 

 seeds which use the automobile for distribution. The fre- 

 quency with which they puncture the tires has caused 

 them to be known as puncture-vines. 



For some reason the ox-eye daisy and the buttercup, so 

 common in the Eastern States, have never penetrated to 

 the rich prairie soils in many parts of the middle west. 

 Here, too, the devil's paint-brush is unknown and the 

 wild carrot is but a name. Ox-eye daisy is so rare that 

 it is cultivated in gardens and has substituted the name 

 of Marguerite for the more usual white weed. 



Other weeds there may be that have not yet appeared 

 for lack of traveling facilities. We have several in- 

 stances of plants that began to move as soon as the way 

 was open. The yellow daisy did not push out from the 

 western plains until the railroads penetrated its territory. 

 The buft'alo burr has a similar history. It is quite likely 

 that the traffic up and down the Mississippi valley is 

 responsible for the presence in most of the Northern 

 .States of a little Mexican weed known as GaJinsfl,c;a. So 

 recent is its coming and so insignificant the plant, that it 

 has not yet acquired a common name. 



In general, weeds are not attractive. Their motto 

 seems to be efficiency and beauty is allowed to take care 

 of itself. Many species, however, are really beautiful if 

 one could forget their weedy c|ualities. The flower- 

 heads of the common bull thistle, the dandelion, the musk 

 mallow and moth mullein, and even the daisy and butter- 

 cup, are good illustrations. Indeed, some of our worst 

 weeds were originally denizens of the flower garden and 

 were only rooted out after they had shown their ignoble 

 natures by rioting afield. Among such are the toad-flax, 

 the little spurge known as graveyard weed, bouncing Bet, 

 chicory and catnip. In the south the really handsome 

 water hyacinth has become an execrated weed because 

 from its very exuberance it thrives so well in certain 

 (Continued on fosf 696") 



