8 THE INDIANA WEED BOOK. 



of many weeds growing on uplands are continually being washed 

 down the slopes into lowland soils where many of them germinate 

 and nourish. So long as careless farmers on the higher grounds 

 allow the seeds of noxious weeds to ripen, just so long will the 

 farmers on the lowlands ha.ve weed seeds scattered over their fields 

 by countless thousands. Many weeds bearing ripened seeds and 

 growing along the banks of streams are washed bodily into the cur- 

 rent when the banks cave off, and are carried for miles down 

 stream, finally lodging in bed of silt or bottom field, in soil well 

 suited to the future plant. 



Birds as seed carriers. — The berries or seed pods of certain 

 weeds are eaten by birds for the nutriment found in the outer pulp 

 and the hard seeds pass undigested. The nightshades, poison ivy, 

 pokeweed, blackberry and pepper-grass are some weeds whose 

 seeds are thus distributed. The seeds- of thistles, ragweeds, dande- 

 lions, knot-grass and other weeds are often eaten in such quantities 

 by sparrows and other birds that many of them are doubtless un- 

 digested and are distributed in new localities. 



"Water birds often carry seeds long distances in mud which 

 has become encased or hardened on their feet. Darwin, in his 

 ' ' Origin of Species, ' ' states that he took in February, 3 tablespoon- 

 fuls of mud from 3 different points beneath water on the edge of 

 a little pond. This mud, when dried, weighed only 6f ounces and 

 in the viscid state was all contained in a breakfast cup. He kept 

 it in his study for six months, pulling up and counting each plant 

 as it grew ; the plants were of many kinds and were altogether 537 

 in number. It is very easy, therefore, for birds to distribute many 

 seeds in this way. 



A bird also sometimes catches up a sprig of a plant and carries 

 it where the seeds can be eaten without molestation, the act re- 

 sulting in a wide scattering of the seed. 



Animals as seed carriers. — Many weeds have developed spines 

 or small hooks on their seeds or seed vessels by which they become 

 attached to the fur of every passing animal, and especially to the 

 wool of sheep, manes of horses and clothing of man, and are then 

 borne far and wide before being dislodged. Thus we have the 

 burs of burdock, cocklebur and bur-grass; the hooked achenes of 

 the buttercups; the barbed hairs of the fruits or seed vessels of 

 wild carrots; the prickly nutlets of hound's tongue and beggars' 

 lice; the bristly pod-joints of the seed-ticks or tick-trefoils and 

 the barbed achenes of the bur-marigolds, beggar-ticks and Spanish 

 needles. The seeds of the mustards, when moistened, exude'a mu- 



