70 VEGETABLE POWER OF ACC0M3I0DATI0N. 



European cardoon, an esculent thistle, has broken out from the 

 gardens of the Spanish colonies on the La Plata, acquired a gi- 

 gantic stature, and propagated itself, in impenetrable thickets, 

 over hundreds of leagues of the Pampas ; and the Anacharis al- 

 sinastrum, a water plant not much inclined to spread in its na- 

 tive American habitat, has found its way into English rivers, and 

 extended itself to such a degree as to form a serious obstruction 

 to the flow of the current, and even to navigation.* This plant 

 was first observed in England in 1827, and soon made its way to 

 the valley of the Rhine. It is now announced as having made 

 its appearance in the Moselle. 



Not only do many wild plants exhibit a remarkable facility of 

 accommodation, but their seeds usually possess great tenacity of 

 life, and their germinating power resists very severe trials. 

 Hence, while the seeds of many cultivated vegetables lose their 

 vitality in two or three years, and can be transported safely to 

 distant countries only with great precautions, the weeds that in- 

 fest those vegetables, though not cared for by man, continue to 

 accompany him in his migrations, and find a new home on every 

 soil he colonizes. 



Indeed, the faculty of spontaneous reproduction and perpetua- 

 tion necessarily supposes a greater power of accommodation, 

 within a certain range, than we find in most domesticated 

 plants ; for it would rarely happen that the seed of a wild plant 

 would fall into ground as nearly similar in composition and con- 

 dition to that whereon its parent grew, as are to each other the 

 soils of different fields artificially prepared for growing a particu- 

 lar vegetable. Accordingly, though every wild species affects a 

 habitat of a particular character, it is found that, if accidentally 

 or designedly sown elsewhere, it will grow under conditions ex- 



* " It is stated by a celebrated English author that the providential spread 

 of the American weed Anacharis alsinastrum has saved thousands of lives by 

 the purifying influence which it has exerted on the watercourses in certain 

 districts in England. These plants liberate oxygen, which attacks poisonous 

 dead organic matter and destroys it, thus ridding the water of its most dan- 

 gerous impurities. It occasionally happens, however, owing perhaps to some 

 peculiarity of the season, that microscopic animals or plants multiply to such 

 an unusual extent in the waters of lakes or rivers as to produce serious annoy- 

 ance. This occurred some years ago in Croton Lake, in the State of New 

 York." 



