TUMBLE-WEEDS 



fallen from heaven, and quite overlooked the fact that this 

 vegetable structure grew and developed (although only in 

 isolated patches and principally as crusts on stones) in the 

 immediate neighbourhood of the spots where they collected 

 it;'i 



Amongst the wind-blown fruits and seeds there are cases in 

 which entire plants are dragged out of the soil and hurried 

 away by the wind, which rolls them over and over. They 

 may be blown along for days together. The seeds drop out 

 by the way. In this country one rarely sees anything of the 

 sort, but in the Prairies of North America, when under 

 cultivation, these tumble-weeds are a serious and expensive 

 pest. Sometimes the farmers dig trenches to catch them, or 

 they may put up fences against which the tumble-weeds 

 become piled or heaped up until they blow over the top. 



It is not very much use to give the names of these weeds, 

 for they are mostly rare or not British species. Such tumble- 

 weeds are generally nearly spherical in general form and 

 have a short, rather weak, root which is easily torn out of 

 the ground. In some grasses, such as " Old Witch," a well- 

 known pest of the United States, the grass-stalk, with many 

 flowers on it, is pulled out of its sheath and blown away. 



But it is more usual for the fruits or seeds themselves to 

 break off the parent plant, and to be carried away by the 

 wind. To this end we find the most extraordinary changes. 

 Although the flower may droop from its stalk, the latter 

 becomes upright and grows quite a considerable length when 

 the seed or fruit is dispatched on its wanderings. This will 

 raise the fruit or seed as high as possible above the sur- 

 rounding grasses. 



Then in some cases the jfruit opens to allow the seed to 



^ Kerner, Natural History of Plants, vol. 2. 

 262 



